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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5. 	int n,k;
  6. 	cin>>n>>k;
  7.  
  8. 	vector<int> numbers(n);
  9.  
  10. 	for(auto& number: numbers){
  11. 		cin>>number;
  12. 	}
  13.  
  14. 	unordered_map<int,int> hashMap;
  15. 	int answer = 0;
  16.  
  17. 	for(int i=0; i<n; i++){
  18.  
  19.  
  20. 		if(hashMap.find(k - numbers[i]) != hashMap.end()){
  21. 			answer+= hashMap[k - numbers[i]];
  22. 		}
  23.  
  24. 		hashMap[numbers[i]]++;
  25. 	}
  26.  
  27. 	cout<<answer;
  28.  
  29. 	return 0;
  30. }
Success #stdin #stdout 0s 5308KB
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stdin
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6 5
2 2 3 3 5 5
stdout
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4
https://ideone.com/ZtVWWE
language:
C++14 (gcc 8.3)
created:
1 day ago
visibility:
public

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