fork download
copy 
  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int ans(vector<int>v,int k){
  5. 	map<int,int>m;
  6. 	int a=0;
  7. 	for(int i=0;i<v.size();i++){
  8. 	     a+=m[k-v[i]];
  9. 		 m[k-v[i]]++;
  10. 	}
  11. 	return a;
  12. }
  13. int main() {
  14. 	// your code goes here
  15. 	int n;cin>>n;
  16. 	vector<int>v(n);
  17. 	for(int i=0;i<n;i++)cin>>v[i];
  18. 	int k;cin>>k;
  19. 	cout<<ans(v,k)<<endl;
  20. 	return 0;
  21. }
Success #stdin #stdout 0.01s 5292KB
comments (?)
stdin
copy 
5
1 2 3 4 5
5
stdout
copy 
0
https://ideone.com/gZge1R
language:
C++14 (gcc 8.3)
created:
6 hours ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!