数算！

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;
+}

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;
+}

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;
+}

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;
+}