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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int ans(vector<int>v,int k){
  5. 	map<int,int>m;int count=0;
  6. 	for(int i=0;i<v.size();i++){
  7. 		int c= k-v[i];
  8. 		if(m[c]>0){
  9. 			count+=m[c];
  10. 		}
  11. 		m[v[i]]++;
  12. 	}
  13. 	return count;
  14.  
  15. }
  16.  
  17. int main() {
  18. 	int n;cin>>n;
  19. 	vector<int>v(n);
  20. 	for(int i=0;i<n;i++)cin>>v[i];
  21. 	int k;cin>>k;
  22. 	cout<<ans(v,k)<<endl;
  23. 	return 0;
  24. }
Success #stdin #stdout 0s 5316KB
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stdin
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4
-2  4 7 -5
2
stdout
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2
https://ideone.com/tUEJYm
language:
C++14 (gcc 8.3)
created:
6 hours ago
visibility:
public

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