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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.             cnt+=it.second*mp[k-it.first];
  17.             mp.erase(k-it.first);
  18.         }
  19.     }
  20.     cout<<cnt<<"\n";
  21. }
Success #stdin #stdout 0.01s 5288KB
comments (?)
stdin
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5 6
1 3 -1 7 5
stdout
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3
https://ideone.com/99H9bo
language:
C++14 (gcc 8.3)
created:
6 days ago
visibility:
public

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