🔴 一份代码，套三种容器

（本条路线统一用 g++ -std=c++17 -O0 -Wall 编译）

#include <iostream>
#include <list>
#include <set>
#include <vector>

/* 一份代码，套三种容器 —— 它只要求"能从头一步步走到尾" */
template <typename It>
int count_above(It first, It last, int line) {
    int n = 0;
    for (It it = first; it != last; ++it) if (*it > line) n++;
    return n;
}

int main() {
    std::vector<int> v{5, 3, 9, 1, 7};
    std::list<int>   l{5, 3, 9, 1, 7};
    std::set<int>    s{5, 3, 9, 1, 7};

    std::cout << count_above(v.begin(), v.end(), 4) << "/"
              << count_above(l.begin(), l.end(), 4) << "/"
              << count_above(s.begin(), s.end(), 4) << "\n";
    return 0;
}