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  1. #include<bits/stdc++.h>
  2. #define LL long long
  3.  
  4. using namespace std;
  5.  
  6. unordered_map<LL, LL>mymap;
  7. LL arr[10002];
  8.  
  9. int main()
  10. {
  11.     int n;
  12.     scanf("%d", &n);
  13.     for(int i=0; i<n; i++){
  14.         scanf("%lld", arr+i);
  15.         mymap[2*arr[i]]++;
  16.     }
  17.  
  18.     LL cnt = 0;
  19.     for(int i=0; i<n; i++){
  20.         for(int j=i+1; j<n; j++){
  21.             LL val = mymap[arr[i] + arr[j]];
  22.             if(val>0) cnt = cnt + val;
  23.             mymap[arr[i] + arr[j]] = 0;
  24.         }
  25.     }
  26.  
  27.     printf("%lld", cnt);
  28. }
  29.  
Success #stdin #stdout 0s 16144KB
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https://ideone.com/ne2rwJ
language:
C++ (gcc 8.3)
created:
6 years ago
visibility:
public

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