fork download
copy 
  1. #include <bits/stdc++.h>
  2. #define endl '\n'
  3. using namespace std;
  4. using ll = long long;
  5.  
  6. int n;
  7. ll ans;
  8. ll a[1000001];
  9. ll pre[1000001];
  10.  
  11. int main(){
  12.     ios_base::sync_with_stdio(false);
  13.     cin.tie(NULL);
  14.     //freopen("MULARR.inp","r",stdin);
  15.     //freopen("MULARR.out","w",stdout);
  16.     cin >> n;
  17.     for(int i = 1; i <= n; i++){
  18.         cin >> a[i];
  19.         pre[i] = pre[i-1] + a[i];
  20.     }
  21.     ans = 0;
  22.     for(int i = 1; i <= n - 1; i++){
  23.         ans += a[i] * (pre[n] - pre[i]);
  24.     }
  25.     cout << ans;
  26.     return 0;
  27. }
  28.  
Success #stdin #stdout 0.01s 5468KB
comments (?)
stdin
copy 
9 4 3 2
stdout
copy 
26
https://ideone.com/6XHNts
language:
C++14 (gcc 8.3)
created:
4 days ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!