Here is the problem:

I don’t know what error I have made. I am getting WA for all test cases. But I get the right answers for sample test cases. I have implemented according to the editorial given.

```
#include<iostream>
#include<stdio.h>
#include<algorithm>
#include<string>
#include<string.h>
#include<math.h>
#include<set>
#include<vector>
#include<utility>
#define MO 1000000007
using namespace std;
int main( ) {
int t;
cin>>t;
long long int n, a[100004],suffix_sum[100004];
long long int cost,prefix;
while ( t-- ) {
cost = 0;
cin>>n;
for ( int i = 0; i <= n; i++ ) {
scanf("%lld", &a[i]);
}
suffix_sum[n] = a[n];
for ( int i = (n-1); i >=1 ; i-- ) {
suffix_sum[i] = ( (long long int)pow(2,(n-i)) * a[i] ) % MO ;
suffix_sum[i] += suffix_sum[i+1];
}
for ( int i = 0; i <= n-1; i++ ) {
if ( i == 0 ) {
prefix = 1;
}
else {
prefix = ( (long long int)pow(2,(i-1)) * a[i] ) % MO;
}
cost += ( (prefix * suffix_sum[i+1]) % MO );
}
cout<<2*cost<<endl;
}
return 0;
}
```