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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4. int a[100001];
  5. int n;
  6. long long f[100001];
  7. long k=0;
  8. long long ans=0;
  9. int main()
  10. {
  11.     cin >> n;
  12.     for(int i=1;i<=n;i++)
  13.     {
  14.         cin >> a[i];
  15.         f[i]=f[i-1]+a[i];
  16.     }
  17.     for(int i=1;i<=n;i++)
  18.     {
  19.         k+=a[1]*a[i]*i;
  20.     }
  21.     ans+=k;
  22.     for(int i=2;i<=n;i++)
  23.     {
  24.         k=k-(a[i-1]*a[i-1]);
  25.         k=k/a[i-1];
  26.         k=k*a[i];
  27.         k=k-a[i]*(f[n]-f[i-1]);
  28.         ans+=k;
  29.     }
  30.     cout << ans;
  31.     return 0;
  32. }
  33.  
Success #stdin #stdout 0.01s 5296KB
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https://ideone.com/bICupp
language:
C++ (gcc 8.3)
created:
5 days ago
visibility:
public

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