some programs!

cs101/dh_20260909_13_flip.cpp

@@ -0,0 +1,39 @@
+#include <iostream>
+
+using namespace std;
+
+constexpr int MAX_N = 151;
+bool cards_flipped[MAX_N];
+
+void simulate() {
+    for (int divider=2; divider<MAX_N; divider++) {
+        for (int i=divider; i<MAX_N; i+=divider) {
+            cards_flipped[i] = !cards_flipped[i];
+        }
+    }
+}
+
+void print_ans() {
+    int amount = 0;
+    bool first = true;
+    for (int i = 1; i < MAX_N; i++) {
+        if (!cards_flipped[i]) {
+            if (!first) cout << " ";
+            cout << "N" << i;
+            first = false;
+            amount++;
+        }
+    }
+    cout << endl << amount << endl;
+}
+
+int main() {
+    ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    simulate();
+    print_ans();
+
+
+    return 0;
+}