std::set_intersection 问题

std::set_intersection 求交的时候，如果传入的是vector 必须要同序

 https://www.programiz.com/cpp-programming/online-compiler/

#include <iostream>
using namespace std;
int main()
{
    cout << "Hello, world!" << endl;
    std::vector<int> exclude_express_province_code_list {31,21};
    std::vector<int> user_city_ids{31,21};
    std::set_intersection(exclude_express_province_code_list.begin(),
                            exclude_express_province_code_list.end(), user_city_ids.begin(),
                            user_city_ids.end(), std::back_inserter(exclude_ids));
    cout << exclude_ids.size();
    return 0;
}

输出2

// Online C++ compiler to run C++ program online
#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <functional>   // std::plus

int main() {
    // Write C++ code here
    // std::cout << "Try programiz.pro";
    std::vector<int> exclude_express_province_code_list {22,31};
    std::vector<int> user_city_ids{31,22};
    std::vector<int> exclude_ids;
    std::set_intersection(exclude_express_province_code_list.begin(),
                            exclude_express_province_code_list.end(), user_city_ids.begin(),
                            user_city_ids.end(), std::back_inserter(exclude_ids));
    std::cout << exclude_ids.size() << std::endl;

    return 0;
}

输出1