diff --git a/.idea/editor.xml b/.idea/editor.xml
index 14cdacd..e956a9f 100644
--- a/.idea/editor.xml
+++ b/.idea/editor.xml
@@ -28,6 +28,22 @@
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppConstValueFunctionReturnType/@EntryIndexedValue" value="SUGGESTION" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppConstexprIfDiscardedBranch/@EntryIndexedValue" value="HINT" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCoroutineCallResolveError/@EntryIndexedValue" value="WARNING" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaConflictingMemorySpaceSpecifiers/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaForLoopCanBeReplacedWithIRange/@EntryIndexedValue" value="SUGGESTION" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaFunctionIsNotCallableFromExecutionSpace/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaGotoStatementIsNotAllowedInTileGlobalFunction/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaGridConstantIsOnlyAllowedOnKernelParameter/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaGridConstantParameterMustBeConstNonReference/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaIRangeStepMustBePositive/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaMemorySpaceLocalVariableMustBeExternOrStatic/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaMemorySpaceSpecifierIsNotAllowedOnDataMember/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaMemorySpaceSpecifierIsNotAllowedOnParameter/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaMemorySpaceSpecifierIsNotAllowedOnTypeAlias/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaMemorySpaceVariableIsNotAllowedInHostFunction/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaReturnStatementInsideLoopIsNotAllowedInTileGlobalFunction/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaSharedVariableCannotHaveInitializer/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaTileKernelLaunchMustHaveBlockSizeOne/@EntryIndexedValue" value="ERROR" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCudaVariableIsNotAccessibleFromExecutionSpace/@EntryIndexedValue" value="ERROR" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDFAArrayIndexOutOfBounds/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDFAConstantConditions/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDFAConstantFunctionResult/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
@@ -205,6 +221,7 @@
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     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppStaticSpecifierOnAnonymousNamespaceMember/@EntryIndexedValue" value="SUGGESTION" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppStringLiteralToCharPointerConversion/@EntryIndexedValue" value="WARNING" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppSyntaxWarning/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppTabsAreDisallowed/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppTemplateArgumentsCanBeDeduced/@EntryIndexedValue" value="HINT" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppTemplateParameterNeverUsed/@EntryIndexedValue" value="HINT" type="string" />
diff --git a/.idea/workspace.xml b/.idea/workspace.xml
index 1034548..2992a5b 100644
--- a/.idea/workspace.xml
+++ b/.idea/workspace.xml
@@ -33,6 +33,7 @@
       <config projectName="exercises" targetName="dp__TJOI2007_walk_segments_dp" />
       <config projectName="exercises" targetName="pojcs101_M02692_12_coins_WRONG" />
       <config projectName="exercises" targetName="pojcs101_M02039_snakey_encryption" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_12_02_count_chars" />
       <config projectName="exercises" targetName="cmake-build-debug-gcc__CMakeFiles__4.3.1__CompilerIdC__CMakeCCompilerId" />
       <config projectName="exercises" targetName="cs101__stage_pre__dh_00_13_flip" />
       <config projectName="exercises" targetName="graph__luogu_P3916_graph_iteration" />
@@ -40,16 +41,19 @@
       <config projectName="exercises" targetName="_others__jzh__jzh_c1_h" />
       <config projectName="exercises" targetName="dp__NOIP1996S_miner_dp_MWASTE" />
       <config projectName="exercises" targetName="pojcs101_T01011_sticks" />
+      <config projectName="exercises" targetName="dsa__ch4_string__luogu_template_kmp_P3375" />
       <config projectName="exercises" targetName="pojcs101_M02431_cows_gas_leak_WRONG" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_05_03_different_num" />
       <config projectName="exercises" targetName="luogu_P1160_biodir_linked_list" />
       <config projectName="exercises" targetName="pojcs101_E01003" />
       <config projectName="exercises" targetName="JLOI2009_binary_tree" />
       <config projectName="exercises" targetName="dsa__ch2_linear_list__dsa_0206_binary_query" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_13_05_books" />
       <config projectName="exercises" targetName="dsa__ch2_linear_list__dsa_0203_string_insertion" />
       <config projectName="exercises" targetName="cs101__stage_pre__dh_00_16_swap_bits" />
       <config projectName="exercises" targetName="pojcs101_T27373_biggest_combination_t2_TLE" />
       <config projectName="exercises" targetName="pojcs101_M02524_ubiquitous_religions_dsu" />
+      <config projectName="exercises" targetName="dsa__ch5_binary_tree__dsa_0510_reconstruct_tree" />
       <config projectName="exercises" targetName="cs101__stage_pre__dh_00_15_jusephus" />
       <config projectName="exercises" targetName="exercises" />
       <config projectName="exercises" targetName="dp__SHOI2002_ski_dp" />
@@ -61,11 +65,14 @@
       <config projectName="exercises" targetName="cs101__stage_1__dh_03_03" />
       <config projectName="exercises" targetName="dsa__ch3_stack_queue__dsa_0302_calculator_WRONG" />
       <config projectName="exercises" targetName="pojcs101_T27104_chicken_monitors" />
+      <config projectName="exercises" targetName="dsa__ch4_string__dsa_0406_valid_string" />
       <config projectName="exercises" targetName="NOIP2016J_bay" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_06_02_convex_polygon" />
       <config projectName="exercises" targetName="pojcs101_T27373_biggest_combination_t2" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_05_01_newton_sqrt" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_12_01_variance" />
       <config projectName="exercises" targetName="_others__others_test_cpp" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_12_05_iter_hui" />
       <config projectName="exercises" targetName="cs101__dh_20260909_11_count_digits" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_01_05_vote" />
       <config projectName="exercises" targetName="cs101__stage_pre__dh_00_14_encryption" />
@@ -73,6 +80,7 @@
       <config projectName="exercises" targetName="cs101__stage_2__dh_11_01_change" />
       <config projectName="exercises" targetName="pojcs101_M01328_radar_greedy_WRONG" />
       <config projectName="exercises" targetName="dp__backpack_dp__NOIP2005J_herbs_dp_knapsack" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_12_04_day_delta" />
       <config projectName="exercises" targetName="dsa__ch2_linear_list__dsa_0202_card_stacking" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_03_05_perfect_cubes" />
       <config projectName="exercises" targetName="pojcs101_M02692_12_coins" />
@@ -83,15 +91,19 @@
       <config projectName="exercises" targetName="pojcs101_E02883" />
       <config projectName="exercises" targetName="dsa__ch2_linear_list__dsa_0217_magic_square" />
       <config projectName="exercises" targetName="cs101__stage_2__dh_11_02_shit_num" />
+      <config projectName="exercises" targetName="dsa__ch4_string__dsa_0404_string_loop" />
       <config projectName="exercises" targetName="dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_MWASTE" />
       <config projectName="exercises" targetName="dp__backpack_dp__NOIP2006S_jinming_budget_dp_knapsack" />
       <config projectName="exercises" targetName="dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_PINGPONG" />
       <config projectName="exercises" targetName="JLOI2009_binary_tree_GIVEUP" />
       <config projectName="exercises" targetName="dsa__ch3_stack_queue__dsa_0306_stack_operation" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_12_03_tumor_detection" />
       <config projectName="exercises" targetName="pojcs101_M03704_brackets" />
       <config projectName="exercises" targetName="pojcs101_M03441_sum_zero" />
       <config projectName="exercises" targetName="pojcs101_M01328_radar_greedy" />
       <config projectName="exercises" targetName="pojcs101_M02746_josephus_problem_simulation" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_13_01_max_points_WRONG" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_12_06_big_binary_addition" />
       <config projectName="exercises" targetName="dsa__ch3_stack_queue__USACO12MARs_flowerpot_WRONG" />
       <config projectName="exercises" targetName="dsa__ch2_linear_list__dsa_0204_prefix_cycle" />
       <config projectName="exercises" targetName="NOIP2003J_bigint" />
@@ -99,6 +111,7 @@
       <config projectName="exercises" targetName="luogu_template_dsu_P3367" />
       <config projectName="exercises" targetName="dsa__ch3_stack_queue__dsa_0302_calculator" />
       <config projectName="exercises" targetName="pojcs101_M03532" />
+      <config projectName="exercises" targetName="dsa__ch5_binary_tree__luogu_P4715_matches" />
       <config projectName="exercises" targetName="cs101__stage_pre__dh_00_12_bottle_exchange" />
       <config projectName="exercises" targetName="pojcs101_M01321_chest_grid" />
       <config projectName="exercises" targetName="cs101__stage_pre__dh_00_10_smaller_numbers" />
@@ -107,6 +120,8 @@
       <config projectName="exercises" targetName="pojcs101_T04117_split_int" />
       <config projectName="exercises" targetName="pojcs101_M01002_memorable_number" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_01_02_subway" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_13_02_tumor_again" />
+      <config projectName="exercises" targetName="dsa__ch5_binary_tree__luogu_T750119_bin_tree_iter" />
       <config projectName="exercises" targetName="pojcs101_M03247_palindromic_prime" />
       <config projectName="exercises" targetName="SHOI2002_ski" />
       <config projectName="exercises" targetName="pojcs101_E01218" />
@@ -121,6 +136,7 @@
       <config projectName="exercises" targetName="cs101__stage_1__dh_05_05_pair_of_shit_nums_ANALYSIS" />
       <config projectName="exercises" targetName="graph__luogu_P3916_graph_iteration_WRONG" />
       <config projectName="exercises" targetName="SHOI2002_ski_WRONG" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_13_06_nums_in_string" />
       <config projectName="exercises" targetName="_others__others_test" />
       <config projectName="exercises" targetName="dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_MWASTE_BETTER" />
       <config projectName="exercises" targetName="cmake-build-debug-gcc__CMakeFiles__4.3.1__CompilerIdCXX__CMakeCXXCompilerId" />
@@ -128,6 +144,8 @@
       <config projectName="exercises" targetName="lc_135_candy" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_05_04_fried_chicken" />
       <config projectName="exercises" targetName="cs101__stage_1__dh_04_01_fibonacci" />
+      <config projectName="exercises" targetName="dsa__ch4_string__dsa_0403_within_string" />
+      <config projectName="exercises" targetName="cs101__stage_2__dh_13_01_max_points" />
       <config projectName="exercises" targetName="graph__USACO06DECs_cow_picnic" />
     </generated>
   </component>
@@ -135,50 +153,29 @@
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-      <change afterPath="$PROJECT_DIR$/cs101/stage_1/dh_05_02_three_nums.cpp" afterDir="false" />
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-      <change afterPath="$PROJECT_DIR$/cs101/stage_1/dh_05_05_pair_of_shit_nums.cpp" afterDir="false" />
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-      <change afterPath="$PROJECT_DIR$/dsa/ch3_stack_queue/USACO12MARs_flowerpot_WRONG.cpp" afterDir="false" />
+    <list default="true" id="4491295e-723c-4e0b-b7b4-9be1cbde5db8" name="更改" comment="some programs!!!">
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+      <change afterPath="$PROJECT_DIR$/cs101/stage_2/dh_12_02_count_chars.cpp" afterDir="false" />
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+      <change afterPath="$PROJECT_DIR$/cs101/stage_2/dh_12_05_iter_hui.cpp" afterDir="false" />
+      <change afterPath="$PROJECT_DIR$/cs101/stage_2/dh_12_06_big_binary_addition.cpp" afterDir="false" />
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+      <change afterPath="$PROJECT_DIR$/cs101/stage_2/dh_13_05_books.cpp" afterDir="false" />
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+      <change afterPath="$PROJECT_DIR$/dsa/ch4_string/dsa_0403_within_string.cpp" afterDir="false" />
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+      <change beforePath="$PROJECT_DIR$/.idea/editor.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/editor.xml" afterDir="false" />
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       <item itemvalue="CMake 应用程序.cs101__stage_pre__dh_00_14_encryption" />
       <item itemvalue="CMake 应用程序.cs101__stage_pre__dh_00_15_jusephus" />
       <item itemvalue="CMake 应用程序.cs101__stage_pre__dh_00_16_swap_bits" />
-      <item itemvalue="CMake 应用程序.cmake-build-debug-gcc__CMakeFiles__4.3.1__CompilerIdC__CMakeCCompilerId" />
-      <item itemvalue="CMake 应用程序.cs101__dh_20260909_11_count_digits_CACHED" />
       <item itemvalue="CMake 应用程序.dp__NOIP1996S_miner_dp_MWASTE" />
       <item itemvalue="CMake 应用程序.dp__NOIP1996S_miner_dp" />
       <item itemvalue="CMake 应用程序.dp__SHOI2002_ski_dp" />
       <item itemvalue="CMake 应用程序.dp__TJOI2007_walk_segments_dp" />
+      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_MWASTE_BETTER" />
+      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_MWASTE" />
+      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_PINGPONG" />
+      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack" />
+      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2006S_jinming_budget_dp_knapsack" />
+      <item itemvalue="CMake 应用程序.dp__eagle_egg" />
+      <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__P2629_good_news" />
+      <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__SDOI2007_queue" />
       <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__dsa_0201_dictionary" />
       <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__dsa_0202_card_stacking" />
       <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__dsa_0203_string_insertion" />
@@ -1094,21 +1220,20 @@
       <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__dsa_0205_polynomial_addition" />
       <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__dsa_0206_binary_query" />
       <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__dsa_0217_magic_square" />
-      <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__P2629_good_news" />
-      <item itemvalue="CMake 应用程序.dsa__ch2_linear_list__SDOI2007_queue" />
-      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0301_sliding_window" />
-      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0301_sliding_window_SLOW" />
-      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0302_calculator" />
-      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0302_calculator_WRONG" />
-      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0306_stack_operation" />
-      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__USACO12MARs_flowerpot" />
       <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__USACO12MARs_flowerpot_WRONG" />
-      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_MWASTE_BETTER" />
-      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_MWASTE" />
-      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack_PINGPONG" />
-      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2005J_herbs_dp_knapsack" />
-      <item itemvalue="CMake 应用程序.dp__backpack_dp__NOIP2006S_jinming_budget_dp_knapsack" />
-      <item itemvalue="CMake 应用程序.dp__eagle_egg" />
+      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__USACO12MARs_flowerpot" />
+      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0301_sliding_window_SLOW" />
+      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0301_sliding_window" />
+      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0302_calculator_WRONG" />
+      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0302_calculator" />
+      <item itemvalue="CMake 应用程序.dsa__ch3_stack_queue__dsa_0306_stack_operation" />
+      <item itemvalue="CMake 应用程序.dsa__ch4_string__dsa_0403_within_string" />
+      <item itemvalue="CMake 应用程序.dsa__ch4_string__dsa_0404_string_loop" />
+      <item itemvalue="CMake 应用程序.dsa__ch4_string__dsa_0406_valid_string" />
+      <item itemvalue="CMake 应用程序.dsa__ch4_string__luogu_template_kmp_P3375" />
+      <item itemvalue="CMake 应用程序.dsa__ch5_binary_tree__dsa_0510_reconstruct_tree" />
+      <item itemvalue="CMake 应用程序.dsa__ch5_binary_tree__luogu_P4715_matches" />
+      <item itemvalue="CMake 应用程序.dsa__ch5_binary_tree__luogu_T750119_bin_tree_iter" />
       <item itemvalue="CMake 应用程序.graph__ECNA2001_sort_letters" />
       <item itemvalue="CMake 应用程序.graph__USACO06DECs_cow_picnic" />
       <item itemvalue="CMake 应用程序.graph__luogu_P3916_graph_iteration_WRONG" />
@@ -1147,8 +1272,8 @@
       <item itemvalue="CMake 应用程序.pojcs101_T27373_biggest_combination_t2_TLE" />
       <item itemvalue="CMake 应用程序.pojcs101_T27373_biggest_combination_t2" />
       <item itemvalue="CMake 应用程序.pojcs101_M02746_josephus_problem_simulation" />
-      <item itemvalue="Python.dh_04_04_balloons_init1" />
       <item itemvalue="Python.NOI2001_food_chain_dsu" />
+      <item itemvalue="Python.dh_04_04_balloons_init1" />
       <item itemvalue="Python.pojcs101_M03247_palindromic_prime_init1" />
     </list>
     <recent_temporary>
@@ -1184,6 +1309,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_12_05_iter_hui",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch3_stack_queue__dsa_0301_sliding_window_SLOW",
@@ -1191,6 +1323,55 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch4_string__dsa_0404_string_loop",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_12_03_tumor_detection",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_12_01_variance",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_13_02_tumor_again",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch4_string__dsa_0406_valid_string",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch5_binary_tree__dsa_0510_reconstruct_tree",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_13_01_max_points",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.luogu_P1160_biodir_linked_list",
@@ -1226,6 +1407,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch4_string__dsa_0403_within_string",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch3_stack_queue__USACO12MARs_flowerpot",
@@ -1233,6 +1421,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_13_05_books",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.pojcs101_T27373_biggest_combination_t2",
@@ -1247,6 +1442,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_12_04_day_delta",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "C/C++ 文件.dh_05_05_pair_of_shit_nums_ANALYSIS.cpp"
@@ -1266,6 +1468,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch4_string__luogu_template_kmp_P3375",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.dp__TJOI2007_walk_segments_dp",
@@ -1273,6 +1482,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.cs101__stage_2__dh_13_06_nums_in_string",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch3_stack_queue__dsa_0306_stack_operation",
@@ -1301,6 +1517,13 @@
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch5_binary_tree__luogu_T750119_bin_tree_iter",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
     {
       "first": {
         "##RUN_CONFIGURATION##": "CMake 应用程序.NOIP2003J_bigint",
@@ -1328,9 +1551,16 @@
         "cmake": "CMakeBuildProfile:Debug-GCC"
       },
       "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
+    },
+    {
+      "first": {
+        "##RUN_CONFIGURATION##": "CMake 应用程序.dsa__ch5_binary_tree__luogu_P4715_matches",
+        "cmake": "CMakeBuildProfile:Debug-GCC"
+      },
+      "second": "2c1c9069-eeff-46e4-9092-db62e2b1ded5"
     }
   ],
-  "modificationCount": 192
+  "modificationCount": 239
 }]]></component>
   <component name="SharedIndexes">
     <attachedChunks>
@@ -1370,7 +1600,8 @@
     <MESSAGE value="some programs" />
     <MESSAGE value="some programs!" />
     <MESSAGE value="some programs!!" />
-    <option name="LAST_COMMIT_MESSAGE" value="some programs!!" />
+    <MESSAGE value="some programs!!!" />
+    <option name="LAST_COMMIT_MESSAGE" value="some programs!!!" />
   </component>
   <component name="XDebuggerManager">
     <breakpoint-manager>
@@ -1425,11 +1656,6 @@
           <line>99</line>
           <option name="timeStamp" value="56" />
         </line-breakpoint>
-        <line-breakpoint enabled="true" type="com.jetbrains.cidr.execution.debugger.OCBreakpointType">
-          <url>file://$PROJECT_DIR$/dsa/ch3_stack_queue/dsa_0302_calculator.cpp</url>
-          <line>102</line>
-          <option name="timeStamp" value="57" />
-        </line-breakpoint>
         <line-breakpoint enabled="true" type="com.jetbrains.cidr.execution.debugger.OCBreakpointType">
           <url>file://$PROJECT_DIR$/dsa/ch2_linear_list/SDOI2007_queue.cpp</url>
           <line>77</line>
@@ -1460,6 +1686,26 @@
           <line>46</line>
           <option name="timeStamp" value="81" />
         </line-breakpoint>
+        <line-breakpoint enabled="true" type="com.jetbrains.cidr.execution.debugger.OCBreakpointType">
+          <url>file://$PROJECT_DIR$/cs101/stage_2/dh_12_01_variance.cpp</url>
+          <line>11</line>
+          <option name="timeStamp" value="82" />
+        </line-breakpoint>
+        <line-breakpoint enabled="true" type="com.jetbrains.cidr.execution.debugger.OCBreakpointType">
+          <url>file://$PROJECT_DIR$/dsa/ch4_string/luogu_template_kmp_P3375.cpp</url>
+          <line>20</line>
+          <option name="timeStamp" value="85" />
+        </line-breakpoint>
+        <line-breakpoint enabled="true" type="com.jetbrains.cidr.execution.debugger.OCBreakpointType">
+          <url>file://$PROJECT_DIR$/dsa/ch5_binary_tree/luogu_P4715_matches.cpp</url>
+          <line>54</line>
+          <option name="timeStamp" value="89" />
+        </line-breakpoint>
+        <line-breakpoint enabled="true" type="com.jetbrains.cidr.execution.debugger.OCBreakpointType">
+          <url>file://$PROJECT_DIR$/dsa/ch5_binary_tree/dsa_0510_reconstruct_tree.cpp</url>
+          <line>34</line>
+          <option name="timeStamp" value="90" />
+        </line-breakpoint>
       </breakpoints>
     </breakpoint-manager>
   </component>
diff --git a/_others/others_test.c b/_others/others_test.c
index c13bdee..a6a961b 100644
--- a/_others/others_test.c
+++ b/_others/others_test.c
@@ -1,21 +1,22 @@
 #include <stdio.h>
 
-#define _NOT_USED \
-'''
-
 int main() {
-    int a, b;
-    scanf("%d%d", &a, &b);
-    printf("%d", a + b);
+    int number = 0, logo = 0;
+    scanf("%d", &number);
+    for (int wait_test = 1; wait_test <= number; wait_test++) {
+        while (logo == 0) {
+            int same = wait_test;
+            while (same >= 67) {
+                int a = same % 100;
+                if (a == 67) {
+                    printf("%d\n", wait_test);
+                    logo++;
+                    break;
+                }
+                same /= 10;
+            }
+        }
+        logo--;
+    }
     return 0;
 }
-
-#define _NOT_USED \
-'''
-
-#define _NOT_USED /*
-
-a, b = map(int, input().split())
-print(a + b)
-
-#*/
diff --git a/_others/others_test_cpp.cpp b/_others/others_test_cpp.cpp
index 076c93f..ea880fe 100644
--- a/_others/others_test_cpp.cpp
+++ b/_others/others_test_cpp.cpp
@@ -1,29 +1,48 @@
-#include <bits/stdc++.h>
+#include <algorithm>
+#include <array>
+#include <iostream>
+#include <vector>
 
-using namespace std;
+constexpr int MAX_N = 1001, MAX_T = 1001;
 
-constexpr float ALLOWED_DIFF = 1e-6;
+struct Attendee {
+    int enter_time = 0, exit_time = 0;
+};
 
-std::tuple<int, double> sqrt_custom(double x) {
-    double est_prev = -1, est_curr = x;
-    int rounds = 0;
-    while (abs(est_curr - est_prev) > ALLOWED_DIFF) {
-        est_prev = est_curr;
-        // est_curr = 0.5 * (est_prev + x / est_prev);
-        est_curr = x / (2 * est_curr) + 0.5 * est_curr;
-        rounds++;
+
+int get_max_attendees_amount(std::vector<Attendee> attendees_schedule) {
+    std::array<int, MAX_T> bucket{};
+    for (const auto [enter_time, exit_time] : attendees_schedule) {
+        for (int t = enter_time; t < exit_time; t++) {
+            bucket[t]++;
+        }
     }
-    return std::make_tuple(rounds, est_curr);
+    return *std::max_element(bucket.begin(), bucket.end());
 }
 
+
 int main() {
-    std::ios::sync_with_stdio(false);
+    std::iostream::sync_with_stdio(false);
     std::cin.tie(nullptr);
+
+    std::vector<Attendee> attendees;
+    char temp_comma;
     int x;
-    while (std::cin >> x) {
-        auto [rounds, ans] = sqrt_custom(x);
-        std::cout << rounds << " " << std::fixed << std::setprecision(2) << ans << std::endl;
+    while (true) {
+        std::cin >> x >> temp_comma;
+        attendees.push_back({x, -1});
+        if (temp_comma != ',') {
+            std::cin.unget();
+            break;
+        }
     }
+    for (int i = 0; i < attendees.size() - 1; i++) {
+        std::cin >> attendees[i].exit_time >> temp_comma;
+    }
+    std::cin >> attendees[attendees.size() - 1].exit_time;
+
+    std::cout << attendees.size() << ' ' << get_max_attendees_amount(attendees) << std::endl;
+
 
     return 0;
 }
diff --git a/cs101/stage_2/dh_12_01_variance.cpp b/cs101/stage_2/dh_12_01_variance.cpp
new file mode 100644
index 0000000..dc76ec5
--- /dev/null
+++ b/cs101/stage_2/dh_12_01_variance.cpp
@@ -0,0 +1,35 @@
+#include <iomanip>
+#include <iostream>
+#include <numeric>
+#include <vector>
+
+double calc_average(const std::vector<double>& nums) {
+    return std::accumulate(nums.begin(), nums.end(), 0.0) / static_cast<double>(nums.size());
+}
+
+double calc_variance(const std::vector<double>& nums) {
+    double avg = calc_average(nums);
+    double accumulated = std::accumulate(
+        nums.begin(), nums.end(),
+        0.0,
+        [avg](double prev, double x) {
+            return prev + (x - avg) * (x - avg);
+        }
+    );
+    return accumulated / static_cast<double>(nums.size());
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::cin >> n;
+    std::vector<double> nums(n);
+    for (int i = 0; i < n; i++) { std::cin >> nums[i]; }
+
+    std::cout << std::fixed << std::setprecision(5)
+        << calc_average(nums) << " " << calc_variance(nums) << std::endl;
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_12_02_count_chars.cpp b/cs101/stage_2/dh_12_02_count_chars.cpp
new file mode 100644
index 0000000..8e511a2
--- /dev/null
+++ b/cs101/stage_2/dh_12_02_count_chars.cpp
@@ -0,0 +1,20 @@
+#include <iostream>
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::string s;
+    std::getline(std::cin, s);
+
+    int uppers_amount = 0, lowers_amount = 0, digits_amount = 0;
+
+    for (char c : s) {
+        if (std::isupper(c)) { uppers_amount++; }
+        if (std::islower(c)) { lowers_amount++; }
+        if (std::isdigit(c)) { digits_amount++; }
+    }
+    std::cout << uppers_amount << " " << lowers_amount << " " << digits_amount << std::endl;
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_12_03_tumor_detection.cpp b/cs101/stage_2/dh_12_03_tumor_detection.cpp
new file mode 100644
index 0000000..e8c076f
--- /dev/null
+++ b/cs101/stage_2/dh_12_03_tumor_detection.cpp
@@ -0,0 +1,66 @@
+#include <array>
+#include <iostream>
+#include <vector>
+
+class Vector2 {
+public:
+    int x = 0, y = 0;
+
+    constexpr Vector2 operator+(const Vector2 other) const {
+        return {x + other.x, y + other.y};
+    }
+};
+
+using TumorGraphLine = std::vector<unsigned short>;
+using TumorGraph = std::vector<TumorGraphLine>;
+
+constexpr int THRESHOLD = 50;
+constexpr std::array<Vector2, 4> DIRS = {Vector2{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
+
+bool is_border(const TumorGraph& tumor_graph, Vector2 pos) {
+    if (tumor_graph[pos.x][pos.y] > THRESHOLD) { return false; }
+    for (const auto dir : DIRS) {
+        Vector2 new_pos = pos + dir;
+        if (tumor_graph[new_pos.x][new_pos.y] > THRESHOLD) { return true; }
+    }
+    return false;
+}
+
+int calc_area(const TumorGraph& tumor_graph) {
+    int area = 0;
+    for (const auto& line : tumor_graph) {
+        for (const auto val : line) {
+            if (val <= THRESHOLD) { area++; }
+        }
+    }
+    return area;
+}
+
+int calc_perimeter(const TumorGraph& tumor_graph) {
+    int perimeter = 0;
+    for (int i = 1; i < tumor_graph.size() - 1; i++) {
+        for (int j = 1; j < tumor_graph.size() - 1; j++) {
+            if (is_border(tumor_graph, {i, j})) { perimeter++; }
+        }
+    }
+    return perimeter;
+}
+
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::cin >> n;
+
+    TumorGraph tumor_graph(n + 2, TumorGraphLine(n + 2, 127));
+    for (int i = 1; i <= n; i++) {
+        for (int j = 1; j <= n; j++) {
+            std::cin >> tumor_graph[i][j];
+        }
+    }
+    std::cout << calc_area(tumor_graph) << ' ' << calc_perimeter(tumor_graph) << std::endl;
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_12_04_day_delta.cpp b/cs101/stage_2/dh_12_04_day_delta.cpp
new file mode 100644
index 0000000..8cd8096
--- /dev/null
+++ b/cs101/stage_2/dh_12_04_day_delta.cpp
@@ -0,0 +1,54 @@
+#include <iostream>
+#include <math.h>
+
+constexpr int DAYS_OF_MONTHS[13] = {-1, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
+
+constexpr bool is_leap(int year) {
+    return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
+}
+
+constexpr int get_days_of_month(int year, int month) {
+    if (month == 2) { return is_leap(year) ? 29 : 28; }
+    return DAYS_OF_MONTHS[month];
+}
+
+constexpr int get_days_of_year(int year) {
+    return is_leap(year) ? 366 : 365;
+}
+
+constexpr int calc_passed_days(int year, int month, int day) {
+    int passed_days = 0;
+    for (int m = 1; m < month; m++) {
+        passed_days += get_days_of_month(year, m);
+    }
+    return passed_days + day;
+}
+
+constexpr int calc_remaining_days(int year, int month, int day) {
+    return get_days_of_year(year) - calc_passed_days(year, month, day);
+}
+
+constexpr int calc_days_delta(int year1, int month1, int day1,
+                              int year2, int month2, int day2) {
+    int days_delta = 0;
+    if (year1 == year2) {
+        return calc_passed_days(year2, month2, day2) - calc_passed_days(year1, month1, day1);
+    }
+    for (int y = year1 + 1; y < year2; y++) {
+        days_delta += get_days_of_year(y);
+    }
+    return days_delta
+        + calc_remaining_days(year1, month1, day1)
+        + calc_passed_days(year2, month2, day2);
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int year1, month1, day1, year2, month2, day2;
+    std::cin >> year1 >> month1 >> day1 >> year2 >> month2 >> day2;
+    std::cout << calc_days_delta(year1, month1, day1, year2, month2, day2) << std::endl;
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_12_05_iter_hui.cpp b/cs101/stage_2/dh_12_05_iter_hui.cpp
new file mode 100644
index 0000000..af911d3
--- /dev/null
+++ b/cs101/stage_2/dh_12_05_iter_hui.cpp
@@ -0,0 +1,73 @@
+#include <iostream>
+#include <vector>
+
+class Vector2 {
+public:
+    int x = 0, y = 0;
+
+    constexpr Vector2 operator+(Vector2 other) const {
+        return {x + other.x, y + other.y};
+    }
+
+    constexpr Vector2 operator+=(Vector2 other) {
+        x += other.x, y += other.y;
+        return *this;
+    }
+
+    constexpr Vector2 rotated(bool clockwise = false) const {
+        if (clockwise) {
+            return {y, -x}; // (2,1) -> (1,-2)
+        }
+        return {-y, x}; // (2,1) -> (-1,2)
+    }
+};
+
+struct GridElement {
+    int value = -1;
+    bool wall = false;
+};
+
+using Grid = std::vector<std::vector<GridElement>>;
+
+Grid get_initial_grid(int h, int w) {
+    Grid grid = Grid(h + 2, std::vector<GridElement>(w + 2));
+    grid[0] = grid[h + 1] = std::vector<GridElement>(w + 2, {.wall = true});
+    for (int i = 1; i < h + 2; i++) {
+        grid[i][0].wall = grid[i][w + 1].wall = true;
+    }
+    return grid;
+}
+
+void move(const Grid& grid, Vector2& pos, Vector2& dir) {
+    Vector2 new_pos = pos + dir;
+    if (grid[new_pos.x][new_pos.y].wall) {
+        dir = dir.rotated(true);
+    }
+    pos += dir;
+}
+
+void iter_and_print_grid(Grid& grid) {
+    Vector2 pos = {1, 1}, dir = {0, 1};
+    for (int _ = 0; _ < (grid.size() - 2) * (grid[0].size() - 2); _++) {
+        std::cout << grid[pos.x][pos.y].value << std::endl;
+        grid[pos.x][pos.y].wall = true;
+        move(grid, pos, dir);
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int h, w;
+    std::cin >> h >> w;
+    Grid grid = get_initial_grid(h, w);
+    for (int i = 1; i <= h; i++) {
+        for (int j = 1; j <= w; j++) {
+            std::cin >> grid[i][j].value;
+        }
+    }
+    iter_and_print_grid(grid);
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_12_06_big_binary_addition.cpp b/cs101/stage_2/dh_12_06_big_binary_addition.cpp
new file mode 100644
index 0000000..7acfe04
--- /dev/null
+++ b/cs101/stage_2/dh_12_06_big_binary_addition.cpp
@@ -0,0 +1,47 @@
+#include <iostream>
+#include <vector>
+
+using BigBin = std::vector<int>;
+
+BigBin plus(BigBin a, const BigBin& b) {
+    if (a.size() < b.size()) { return plus(b, a); }
+    for (int i = 0; i < b.size(); i++) {
+        a[i] += b[i];
+    }
+    a.push_back(0);
+    for (int i = 1; i < a.size(); i++) {
+        if (a[i - 1] > 1) { a[i - 1] -= 2, a[i]++; }
+    }
+    while (a.back() == 0) { a.pop_back(); }
+    return a;
+}
+
+BigBin parse_string(const std::string s) {
+    BigBin big_bin(s.size());
+    for (int i = 0; i < s.size(); i++) {
+        big_bin[i] = s[s.size() - i - 1] - '0';
+    }
+    return big_bin;
+}
+
+std::ostream& operator<<(std::ostream& os, const BigBin& big_bin) {
+    for (int i = big_bin.size() - 1; i >= 0; i--) {
+        os << big_bin[i];
+    }
+    return os;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::string s1, s2;
+    std::cin >> n;
+    for (int _ = 0; _ < n; _++) {
+        std::cin >> s1 >> s2;
+        std::cout << plus(parse_string(s1), parse_string(s2)) << std::endl;
+    }
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_13_01_max_points.cpp b/cs101/stage_2/dh_13_01_max_points.cpp
new file mode 100644
index 0000000..88ad326
--- /dev/null
+++ b/cs101/stage_2/dh_13_01_max_points.cpp
@@ -0,0 +1,47 @@
+#include <algorithm>
+#include <array>
+#include <iostream>
+
+constexpr int GRID_SIZE = 101;
+std::array<std::array<bool, GRID_SIZE>, GRID_SIZE> has_point, is_invalid;
+
+void add_point(int x, int y) {
+    has_point[x][y] = true;
+    for (int i = 0; i <= x; i++) {
+        for (int j = 0; j <= y; j++) {
+            if (i == x && j == y) { break; }
+            is_invalid[i][j] = true;
+        }
+    }
+}
+
+void print_ans() {
+    bool first = true;
+    for (int i = 0; i < GRID_SIZE; i++) {
+        for (int j = 0; j < GRID_SIZE; j++) {
+            if (has_point[i][j] && !is_invalid[i][j]) {
+                if (!first) { std::cout << ','; }
+                std::cout << '(' << i << ',' << j << ')';
+                first = false;
+            }
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::cin >> n;
+
+    for (int _ = 0; _ < n; _++) {
+        int x, y;
+        std::cin >> x >> y;
+        add_point(x, y);
+    }
+
+    print_ans();
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_13_01_max_points_WRONG.cpp b/cs101/stage_2/dh_13_01_max_points_WRONG.cpp
new file mode 100644
index 0000000..3488651
--- /dev/null
+++ b/cs101/stage_2/dh_13_01_max_points_WRONG.cpp
@@ -0,0 +1,60 @@
+#include <algorithm>
+#include <array>
+#include <iostream>
+
+constexpr int GRID_SIZE = 101;
+std::array<std::array<bool, GRID_SIZE>, GRID_SIZE> grid;
+std::array<int, GRID_SIZE> row_maxs, col_maxs;
+bool has_0_0 = false;
+
+void init_maxs() {
+    for (int i = 0; i < GRID_SIZE; i++) {
+        for (int j = GRID_SIZE - 1; j >= 0; j--) {
+            if (grid[i][j]) {
+                row_maxs[i] = j;
+                break;
+            }
+        }
+    }
+    for (int j = 0; j < GRID_SIZE; j++) {
+        for (int i = GRID_SIZE - 1; i >= 0; i--) {
+            if (grid[i][j]) {
+                col_maxs[j] = i;
+                break;
+            }
+        }
+    }
+}
+
+void print_ans() {
+    bool first = true;
+    for (int i = 0; i < GRID_SIZE; i++) {
+        int j = row_maxs[i];
+        if (col_maxs[j] == i) {
+            if (i == 0 && j == 0 && !has_0_0) { continue; }
+            if (!first) { std::cout << ','; }
+            std::cout << '(' << i << ',' << j << ')';
+            first = false;
+        }
+    }
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::cin >> n;
+
+    for (int _ = 0; _ < n; _++) {
+        int x, y;
+        std::cin >> x >> y;
+        grid[x][y] = true;
+        if (x == 0 && y == 0) { has_0_0 = true; }
+    }
+
+    init_maxs();
+    print_ans();
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_13_02_tumor_again.cpp b/cs101/stage_2/dh_13_02_tumor_again.cpp
new file mode 100644
index 0000000..a547cd7
--- /dev/null
+++ b/cs101/stage_2/dh_13_02_tumor_again.cpp
@@ -0,0 +1,35 @@
+#include <iostream>
+
+using Coord = std::pair<int, int>;
+
+constexpr int INF = 0x3f3f3f3f;
+Coord top_left = {INF, INF}, bottom_right = {-INF, -INF};
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::cin >> n;
+
+    for (int i = 0; i < n; i++) {
+        for (int j = 0; j < n; j++) {
+            int x;
+            std::cin >> x;
+            if (x != 0) { continue; }
+            top_left = std::min(top_left, {i, j});
+            bottom_right = std::max(bottom_right, {i, j});
+            // top_left.first = std::min(top_left.first,i);
+            // top_left.second = std::min(top_left.second,j);
+            // bottom_right.first = std::max(bottom_right.first,i);
+            // bottom_right.second = std::max(bottom_right.second,j);
+        }
+    }
+    std::cout
+        << std::max(
+            (bottom_right.first - top_left.first - 1) * (bottom_right.second - top_left.second - 1)
+            , 0)
+        << std::endl;
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_13_05_books.cpp b/cs101/stage_2/dh_13_05_books.cpp
new file mode 100644
index 0000000..c6dd938
--- /dev/null
+++ b/cs101/stage_2/dh_13_05_books.cpp
@@ -0,0 +1,36 @@
+#include <algorithm>
+#include <array>
+#include <iostream>
+#include <vector>
+
+constexpr int AUTHORS_AMOUNT = 26;
+std::array<std::vector<int>, AUTHORS_AMOUNT> books_of_authors;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int books_amount;
+    std::cin >> books_amount;
+
+    for (int _ = 0; _ < books_amount; _++) {
+        int book_id;
+        std::string authors;
+        std::cin >> book_id >> authors;
+        for (char c : authors) {
+            books_of_authors[c - 'A'].push_back(book_id);
+        }
+    }
+
+    auto best_author = std::max_element(books_of_authors.begin(), books_of_authors.end(),
+                                        [](const auto& a, const auto& b) {
+                                            return a.size() < b.size();
+                                        });
+    std::cout << static_cast<char>(best_author - books_of_authors.begin() + 'A') << std::endl
+        << best_author->size() << std::endl;
+    for (auto book : *best_author) {
+        std::cout << book << std::endl;
+    }
+
+    return 0;
+}
diff --git a/cs101/stage_2/dh_13_06_nums_in_string.cpp b/cs101/stage_2/dh_13_06_nums_in_string.cpp
new file mode 100644
index 0000000..6e3e171
--- /dev/null
+++ b/cs101/stage_2/dh_13_06_nums_in_string.cpp
@@ -0,0 +1,38 @@
+#include <algorithm>
+#include <iostream>
+#include <vector>
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::vector<int> numbers;
+    int chr;
+    bool in_number = false;
+    while ((chr = std::getchar()) != EOF && chr != '\n') {
+        char c = static_cast<char>(chr);
+        if (!isdigit(c)) {
+            in_number = false;
+            continue;
+        }
+        if (in_number) {
+            numbers.back() = numbers.back() * 10 + (c - '0');
+        } else {
+            in_number = true;
+            numbers.push_back(c - '0');
+        }
+    }
+    std::sort(numbers.begin(), numbers.end());
+    bool first_flag = true;
+    for (int x : numbers) {
+        if (!first_flag) { std::cout << ','; }
+        std::cout << x;
+        first_flag = false;
+    }
+    if (first_flag) {
+        std::cout << 0 << std::endl;
+    }
+
+
+    return 0;
+}
diff --git a/dsa/ch4_string/dsa_0403_within_string.cpp b/dsa/ch4_string/dsa_0403_within_string.cpp
new file mode 100644
index 0000000..d38511a
--- /dev/null
+++ b/dsa/ch4_string/dsa_0403_within_string.cpp
@@ -0,0 +1,20 @@
+#include <iostream>
+
+bool is_within(const std::string& str, const std::string& substr) {
+    int i = 0, j = 0;
+    for (; i < str.size() && j < substr.size(); i++) {
+        if (str[i] == substr[j]) { j++; }
+    }
+    return j == substr.size();
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+    std::string substr, str;
+    while (std::cin >> substr >> str) {
+        std::cout << (is_within(str, substr) ? "Yes" : "No") << std::endl;
+    }
+
+    return 0;
+}
diff --git a/dsa/ch4_string/dsa_0404_string_loop.cpp b/dsa/ch4_string/dsa_0404_string_loop.cpp
new file mode 100644
index 0000000..181b187
--- /dev/null
+++ b/dsa/ch4_string/dsa_0404_string_loop.cpp
@@ -0,0 +1,47 @@
+#include <iostream>
+#include <vector>
+
+std::ostream& operator<<(std::ostream& os, const std::vector<int>& vector) {
+    for (const auto elem : vector) {
+        os << elem << ' ';
+    }
+    return os;
+}
+
+std::vector<int> prefix_function(const std::string& s) {
+    std::vector<int> pi(s.size());
+    for (int i = 1; i < s.size(); i++) {
+        int j = pi[i - 1];
+        while (true) {
+            if (s[i] == s[j]) {
+                pi[i] = j + 1;
+                break;
+            }
+            if (j == 0) {
+                pi[i] = 0;
+                break;
+            }
+            j = pi[j - 1];
+        }
+    }
+    return pi;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::string s;
+    while (std::cin >> s && s != ".") {
+        auto pi = prefix_function(s);
+        std::clog << pi << std::endl;
+        int period = static_cast<int>(s.size()) - pi.back();
+        if (s.size() % period != 0) {
+            std::cout << 1 << std::endl;
+        } else {
+            std::cout << s.size() / period << std::endl;
+        }
+    }
+
+    return 0;
+}
diff --git a/dsa/ch4_string/dsa_0406_valid_string.cpp b/dsa/ch4_string/dsa_0406_valid_string.cpp
new file mode 100644
index 0000000..0f5c0de
--- /dev/null
+++ b/dsa/ch4_string/dsa_0406_valid_string.cpp
@@ -0,0 +1,58 @@
+#include <iostream>
+#include <regex>
+
+bool matches(std::string s, std::string pattern) {
+    int i = 0, j = 0;
+    bool within_bracket = false;
+    while (true) {
+        if (!within_bracket) {
+            if (pattern[j] == '[') {
+                within_bracket = true;
+                j++;
+                continue;
+            }
+            if (s[i] != pattern[j]) { return false; }
+            i++, j++;
+        } else {
+            bool matched = false;
+            while (pattern[j] != ']') {
+                matched = s[i] == pattern[j] || matched;
+                within_bracket = false;
+                j++;
+            }
+            if (!matched) { return false; }
+            i++, j++;
+        }
+        if (i == s.size() && j == pattern.size()) { return true; }
+        if (i == s.size() || j == pattern.size()) { return false; }
+    }
+    throw std::logic_error("What the fuck is this piece of WCJ doing?");
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+    int n;
+    std::string pattern;
+    std::cin >> n;
+    std::vector<std::string> strs(n);
+    for (int i = 0; i < n; i++) {
+        std::cin >> strs[i];
+    }
+    std::cin >> pattern;
+    for (char& c : pattern) {
+        if (std::isupper(c)) { c -= 'A' - 'a'; }
+    }
+
+    for (int i = 0; i < n; i++) {
+        std::string s = strs[i];
+        for (char& c : s) {
+            if (std::isupper(c)) { c -= 'A' - 'a'; }
+        }
+        if (matches(s, pattern)) {
+            std::cout << i + 1 << ' ' << strs[i] << std::endl;
+        }
+    }
+
+    return 0;
+}
diff --git a/dsa/ch4_string/luogu_template_kmp_P3375.cpp b/dsa/ch4_string/luogu_template_kmp_P3375.cpp
new file mode 100644
index 0000000..4c9e2ca
--- /dev/null
+++ b/dsa/ch4_string/luogu_template_kmp_P3375.cpp
@@ -0,0 +1,49 @@
+#include <iostream>
+#include <vector>
+
+std::vector<int> prefix_function(const std::string& s) {
+    std::vector<int> pi(s.size());
+    for (int i = 1; i < s.size(); i++) {
+        int j = pi[i - 1];
+        while (j > 0 && s[i] != s[j]) {
+            j = pi[j - 1];
+        }
+        if (s[i] == s[j]) { j++; }
+        pi[i] = j;
+    }
+    return pi;
+}
+
+std::vector<int> find_substring_pos(const std::string& target, const std::string& pattern) {
+    std::vector<int> matched_pos;
+    const std::vector<int> pattern_prefix_values = prefix_function(pattern);
+    int j = 0;
+    for (int i = 0; i < target.size(); i++) {
+        while (j > 0 && target[i] != pattern[j]) {
+            j = pattern_prefix_values[j - 1];
+        }
+        if (target[i] == pattern[j]) { j++; }
+        if (j == pattern.size()) {
+            matched_pos.push_back(i - static_cast<int>(pattern.size()) + 1);
+            j = pattern_prefix_values[j - 1];
+        }
+    }
+    return matched_pos;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::string target, pattern;
+    std::cin >> target >> pattern;
+    for (const auto i : find_substring_pos(target, pattern)) {
+        std::cout << i + 1 << std::endl;
+    }
+    for (const auto val : prefix_function(pattern)) {
+        std::cout << val << " ";
+    }
+    std::cout << std::endl;
+
+    return 0;
+}
diff --git a/dsa/ch5_binary_tree/dsa_0510_reconstruct_tree.cpp b/dsa/ch5_binary_tree/dsa_0510_reconstruct_tree.cpp
new file mode 100644
index 0000000..08f55d6
--- /dev/null
+++ b/dsa/ch5_binary_tree/dsa_0510_reconstruct_tree.cpp
@@ -0,0 +1,106 @@
+#include <cassert>
+#include <iostream>
+#include <vector>
+#include <algorithm>
+#include <sstream>
+
+class BinaryTree {
+public:
+    struct Node {
+        int value = -1;
+        Node *father = nullptr, *left = nullptr, *right = nullptr;
+    };
+
+    Node* root = nullptr;
+
+    void reconstruct(const std::vector<int>& inorder_traversal, const std::vector<int>& postorder_traversal) {
+        assert(inorder_traversal.size() == postorder_traversal.size());
+        root = reconstruct_node(
+            inorder_traversal, postorder_traversal,
+            0, inorder_traversal.size(),
+            0, inorder_traversal.size());
+    }
+
+    [[nodiscard]] std::vector<int> preorder_traversal() {
+        std::vector<int> result;
+        preorder_dfs(root, result);
+        return result;
+    }
+
+protected:
+    Node* reconstruct_node(
+        const std::vector<int>& inorder_traversal, const std::vector<int>& postorder_traversal,
+        std::size_t inorder_begin, std::size_t inorder_end, std::size_t postorder_begin, std::size_t postorder_end
+    ) {
+        if (inorder_end - inorder_begin == 1) {
+            return new Node({.value = inorder_traversal[inorder_begin]});
+        }
+        if (inorder_end == inorder_begin) { return nullptr; }
+        auto in_begin = inorder_traversal.begin() + inorder_begin;
+        auto in_end = inorder_traversal.begin() + inorder_end;
+        auto root_idx = std::find(
+            in_begin, in_end,
+            postorder_traversal[postorder_end - 1]
+        ) - inorder_traversal.begin();
+        auto left_length = root_idx - inorder_begin;
+        auto right_length = inorder_end - root_idx - 1;
+
+        Node* left_node = reconstruct_node(
+            inorder_traversal, postorder_traversal,
+            inorder_begin, root_idx, postorder_begin, postorder_begin + left_length
+        );
+        Node* right_node = reconstruct_node(
+            inorder_traversal, postorder_traversal,
+            root_idx + 1, inorder_end, postorder_end - 1 - right_length, postorder_end - 1
+        );
+
+        Node* node = new Node({
+            .value = inorder_traversal[root_idx],
+            .left = left_node, .right = right_node,
+        });
+        if (left_node != nullptr) { left_node->father = node; }
+        if (right_node != nullptr) { right_node->father = node; }
+        return node;
+    }
+
+    void preorder_dfs(Node* node, std::vector<int>& result) {
+        if (node == nullptr) { return; }
+        result.push_back(node->value);
+        preorder_dfs(node->left, result);
+        preorder_dfs(node->right, result);
+    }
+};
+
+
+std::ostream& operator<<(std::ostream& os, const std::vector<int>& vector) {
+    for (int x : vector) { os << x << ' '; }
+    return os;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::vector<int> inorder_traversal, postorder_traversal;
+
+    std::string lines[2];
+    std::getline(std::cin, lines[0]);
+    std::getline(std::cin, lines[1]);
+
+    std::istringstream iss1(lines[0]), iss2(lines[1]);
+    int temp;
+    while (iss1 >> temp) {
+        inorder_traversal.push_back(temp);
+    }
+    while (iss2 >> temp) {
+        postorder_traversal.push_back(temp);
+    }
+
+    std::clog << inorder_traversal << std::endl << postorder_traversal << std::endl;
+
+    BinaryTree binary_tree;
+    binary_tree.reconstruct(inorder_traversal, postorder_traversal);
+    std::cout << binary_tree.preorder_traversal() << std::endl;
+
+    return 0;
+}
diff --git a/dsa/ch5_binary_tree/luogu_P4715_matches.cpp b/dsa/ch5_binary_tree/luogu_P4715_matches.cpp
new file mode 100644
index 0000000..6d99dab
--- /dev/null
+++ b/dsa/ch5_binary_tree/luogu_P4715_matches.cpp
@@ -0,0 +1,62 @@
+#include <cmath>
+#include <functional>
+#include <iostream>
+
+class BinaryTree {
+public:
+    struct Node {
+        int value = -1;
+        Node *father = nullptr, *left = nullptr, *right = nullptr;
+        int depth = -1;
+    };
+
+    Node* root = new Node({.depth = 0});
+
+    void init_full_tree(int height, const std::function<bool(int, int)>& comp) {
+        int id = 0;
+        return init_full_tree(height, comp, 0, nullptr, id);
+    }
+
+protected:
+    void init_full_tree(int height, const std::function<bool(int, int)>& comp,
+                        int current_depth, Node* current_node, int& id) {
+        if (current_depth == 0) { current_node = root; }
+        if (current_depth == height) {
+            current_node->value = id++;
+            return;
+        }
+        current_node->left = new Node();
+        current_node->right = new Node();
+        init_full_tree(height, comp, current_depth + 1, current_node->left, id);
+        init_full_tree(height, comp, current_depth + 1, current_node->right, id);
+        if (comp(current_node->left->value, current_node->right->value)) {
+            current_node->value = current_node->right->value;
+        } else {
+            current_node->value = current_node->left->value;
+        }
+    }
+};
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    BinaryTree binary_tree;
+    std::vector<int> strengths;
+    std::cin >> n;
+    strengths.resize(static_cast<std::size_t>(std::pow(2, n)));
+    for (int& strength : strengths) { std::cin >> strength; }
+    binary_tree.init_full_tree(n,
+                               [strengths](int i, int j) {
+                                   return strengths[i] < strengths[j];
+                               });
+    // std::cout << binary_tree.root->value << std::endl;
+    int gold = binary_tree.root->value;
+    int silver = binary_tree.root->left->value == gold
+                     ? binary_tree.root->right->value
+                     : binary_tree.root->left->value;
+    std::cout << silver + 1 << std::endl;
+
+    return 0;
+}
diff --git a/dsa/ch5_binary_tree/luogu_T750119_bin_tree_iter.cpp b/dsa/ch5_binary_tree/luogu_T750119_bin_tree_iter.cpp
new file mode 100644
index 0000000..8fc4bbf
--- /dev/null
+++ b/dsa/ch5_binary_tree/luogu_T750119_bin_tree_iter.cpp
@@ -0,0 +1,103 @@
+#include <iostream>
+#include <vector>
+
+constexpr int MAX_N = 1e5 + 1;
+
+class BinaryTree {
+public:
+    using NodeIdx = int;
+
+    struct Node {
+        NodeIdx father = -1, left = -1, right = -1;
+    };
+
+    NodeIdx root = -1;
+    std::vector<Node> nodes;
+
+    explicit BinaryTree(int n) : nodes(n) {}
+
+    NodeIdx init_root() {
+        root = 0;
+        while (nodes[root].father != -1) {
+            root = nodes[root].father;
+        }
+        return root;
+    }
+
+    [[nodiscard]] std::vector<int> preorder_traversal() {
+        std::vector<int> result;
+        result.reserve(nodes.size());
+        preorder_dfs(root, result);
+        return result;
+    }
+
+    [[nodiscard]] std::vector<int> postorder_transversal() {
+        std::vector<int> result;
+        result.reserve(nodes.size());
+        postorder_dfs(root, result);
+        return result;
+    }
+
+    [[nodiscard]] std::vector<int> inorder_transversal() {
+        std::vector<int> result;
+        result.reserve(nodes.size());
+        inorder_dfs(root, result);
+        return result;
+    }
+
+protected:
+    void preorder_dfs(NodeIdx node, std::vector<int>& result) {
+        if (node == -1) { return; }
+        result.push_back(node);
+        preorder_dfs(nodes[node].left, result);
+        preorder_dfs(nodes[node].right, result);
+    }
+
+    void postorder_dfs(NodeIdx node, std::vector<int>& result) {
+        if (node == -1) { return; }
+        postorder_dfs(nodes[node].left, result);
+        postorder_dfs(nodes[node].right, result);
+        result.push_back(node);
+    }
+
+    void inorder_dfs(NodeIdx node, std::vector<int>& result) {
+        if (node == -1) { return; }
+        inorder_dfs(nodes[node].left, result);
+        result.push_back(node);
+        inorder_dfs(nodes[node].right, result);
+    }
+};
+
+std::ostream& operator<<(std::ostream& os, const std::vector<int>& vector) {
+    for (int x : vector) { os << x + 1 << ' '; }
+    return os;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n;
+    std::cin >> n;
+
+    BinaryTree binary_tree(n);
+
+    for (int i = 0; i < n; i++) {
+        int x, y;
+        std::cin >> x >> y;
+        x--, y--;
+
+        binary_tree.nodes[i].left = x;
+        binary_tree.nodes[i].right = y;
+        if (x >= 0) { binary_tree.nodes[x].father = i; }
+        if (y >= 0) { binary_tree.nodes[y].father = i; }
+    }
+
+    binary_tree.init_root();
+
+    std::cout << binary_tree.preorder_traversal() << std::endl;
+    std::cout << binary_tree.inorder_transversal() << std::endl;
+    std::cout << binary_tree.postorder_transversal() << std::endl;
+
+    return 0;
+}