⚠️ 拼一串，一次都不拷

（本条路线统一用 g++ -std=c++17 -O0 -Wall 编译）注意循环变量的写法：

#include <iostream>
#include <string>
#include <vector>

int main() {
    std::vector<std::string> parts{"a", "bb", "ccc"};

    std::string joined;
    for (const std::string &p : parts) {      /* const& ：一次都不拷 */
        if (!joined.empty()) joined += "-";
        joined += p;
    }

    std::cout << joined << "/" << joined.size() << "\n";
    return 0;
}