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  1. #include<bits/stdc++.h>
  2. #define int long long 
  3. #define endl "\n"
  4. using namespace std;
  5. const int MOD=1e9+7;
  6. int n,i,a[200001],t[200002]={},kq=0;
  7. signed main()
  8. {
  9. 	cin>>n;
  10. 	for(i=1;i<=n;i++) cin>>a[i];
  11. 	for(i=n;i>=1;i--) t[i]=(t[i+1]+a[i])%MOD;
  12. 	for(i=1;i<=n;i++)
  13. 	{
  14. 		kq=(kq+(a[i]*t[i+1])%MOD)%MOD; 
  15. //		cout<<kq<<endl;
  16. 	}
  17. 	cout<<kq;
  18. }
Success #stdin #stdout 0s 5316KB
comments (?)
stdin 
3
1 2 3
stdout 
11
https://ideone.com/mqZRW9
language:
C++14 (gcc 8.3)
created:
333 days ago
visibility:
secret

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