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  1. #include <algorithm>
  2. #include<iostream>
  3. #include <cstdio>
  4. #include <ctime>
  5. #include <vector>
  6. #include <complex>
  7. using namespace std;
  8. #define cd complex<double>
  9. #define vcd vector<cd>
  10. #define si(n) scanf("%d",&n)
  11. #define f(i,a,b) for(int i=a;i<b;i++)
  12. #define pb push_back
  13. #define PI 3.1415926535897932384626433832795
  14. #define mm 30001
  15. #define LL long long
  16. int prev[mm],next[mm];
  17.  
  18. int main()
  19. {
  20.     int n;
  21.     si(n);
  22.     int A[n];
  23.     f(i,0,n)
  24.     {
  25.         si(A[i]);
  26.         next[A[i]]++;
  27.     }
  28.     LL cnt=0;
  29.     f(j,0,n)
  30.     {
  31.         next[A[j]]--;
  32.         for(int i=max(1,2*A[j]-30000);i<=min(30000,2*A[j]-1);i++)
  33.         {
  34.             cnt+=(LL)prev[i]*next[2*A[j]-i];
  35.         }
  36.         prev[A[j]]++;
  37.     }
  38.     printf("%lld\n",cnt);
  39.     return 0;
  40. }
  41.  
Runtime error #stdin #stdout 0.02s 2956KB
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Standard input is empty
stdout
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Standard output is empty
https://ideone.com/RjIOGG
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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