编辑代码

#include <iostream>
#include <vector>

int main() {
    std::vector<int> people;
    for (int i = 1; i <= 21; i++) {
        people.push_back(i);
    }

    int count = 0;
    while (people.size() > 1) {
        for (size_t i = 0; i < people.size(); i++) {
            count++;
            if (count % 5 == 0) {
                people.erase(people.begin() + i);
                i--;
            }
        }
    }
    std::cout << people[0] << std::endl;

    return 0;
}