1.函数   std::next_permutation(first, last)

2.用法的前提下是序列在有序的情况下；

#include <algorithm>
#include <string>
#include <iostream>

int main()
{
    std::string s = "abc";
    std::sort(s.begin(), s.end());
    do {
        std::cout << s << '\n';
    } while(std::next_permutation(s.begin(), s.end()));
}
/*
output:
abc
acb
bac
bca
cab
cba
*/