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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. const int N=1e6+4;
  4. long long n,k;
  5. map<long long,long long>mp;
  6. int main()
  7. {
  8.     long long dem=0;
  9.     cin>>n>>k;
  10.     for(int i=1;i<=n;i++)
  11.     {
  12.         long long x;
  13.         cin>>x;
  14.         dem+=mp[k-x];
  15.         mp[x]++;
  16.     }
  17.     cout<<dem;
  18. }
  19.  
Success #stdin #stdout 0.01s 5476KB
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https://ideone.com/oY5zkF
language:
C++14 (gcc 8.3)
created:
1 year ago
visibility:
public

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