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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. int countPairs(vector<int>&b,int k){
  4.     unordered_map<int,int>f;
  5.     int cnt=0;
  6.     for(int i=0;i<b.size();i++){
  7.         int complement=k-b[i];
  8.         if(f.find(complement)!=f.end())cnt+=f[complement];
  9.         f[b[i]]++;
  10.     }
  11.     return cnt;
  12. }
  13. int main(){
  14.     vector<int>b={1,2,3,4,3};int k=6;
  15.     cout<<countPairs(b,k)<<"\n";
  16.     return 0;
  17. }
  18.  
Success #stdin #stdout 0.01s 5280KB
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https://ideone.com/DjOEwd
language:
C++ (gcc 8.3)
created:
4 days ago
visibility:
public

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