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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. main(){
  5.     int n,k;
  6.     cin>>n>>k;
  7.     vector<int>v(n);
  8.     unordered_map<int,int>mp;
  9.     for(auto &it:v){
  10.         cin>>it;
  11.         mp[it]++;
  12.     }
  13.     int cnt=0;
  14.     for(auto &it:mp){
  15.         if(mp.find(k-it.first)!=mp.end()){
  16.             if(k-it.first!=it.first){
  17.                 cnt+=it.second*mp[k-it.first];
  18.                 mp.erase(k-it.first);
  19.             }
  20.         }
  21.     }
  22.     cout<<cnt<<"\n";
  23. }
Success #stdin #stdout 0.01s 5292KB
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stdin
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5 6
1 3 -1 7 5
stdout
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2
https://ideone.com/J5CWQF
language:
C++14 (gcc 8.3)
created:
6 days ago
visibility:
public

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