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;
+}