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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. int main() {
  5. 	int k;cin>>k;
  6. int n; cin>>n;
  7. int f=0;
  8. unordered_map<int,int> mp;
  9. for(int i=0;i<n;i++){
  10. int t; cin>>t;
  11.  
  12.    f+=(mp[k-t]),mp[t]++;
  13.  
  14. }
  15. cout<<f;
  16. }
Success #stdin #stdout 0.01s 5276KB
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5
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0 5 1 4 4 1 5 5 5 5
stdout
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9
https://ideone.com/fNw7BO
2
language:
C++14 (gcc 8.3)
created:
12 hours ago
visibility:
public

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