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

 

源码

template <class InputIterator1, class InputIterator2, class OutputIterator>
OutputIterator set_intersection (InputIterator1 first1, InputIterator1 last1,
                                 InputIterator2 first2, InputIterator2 last2,
                                 OutputIterator result)
{
  while (first1!=last1 && first2!=last2)
  {
    if (*first1<*first2) ++first1;
    else if (*first2<*first1) ++first2;
    else {
      *result = *first1;
      ++result; ++first1; ++first2;
    }
  }
  return result;
}

 

 

 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