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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int twoSum(vector<int>& a , int target){
  5. 	unordered_map<int,int>mpp;
  6. 	int ans = 0;
  7. 	for(int i=0;i<a.size();i++){
  8. 		int comp = target-a[i];
  9. 		if(mpp.count(comp)){
  10. 			ans += mpp[comp];
  11. 		}
  12. 		mpp[a[i]]++;
  13. 	}
  14. 	return ans;
  15. }
  16.  
  17. int main() {
  18.     int n;
  19.     cin >> n;
  20.     vector<int> arr(n);
  21.  
  22.     for (int i = 0; i < n; i++) {
  23.         cin >> arr[i];
  24.     }
  25.  
  26.     int target;
  27.     cin >> target;
  28.  
  29.     cout << (twoSum(arr, target));
  30.     return 0;
  31. }
  32.  
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/Y5lF70
language:
C++ (gcc 8.3)
created:
38 days ago
visibility:
public

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