This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld double
const int INF = 1e18;
const int mod = 1e9 + 7;
const int sz = 5e5 + 5;
int mod_exp(int a , int b , int c)
{
int res = 1;
a = a % c;
while(b > 0){
if(b & 1) res = (res * a) % c;
b /= 2;
a = (a * a) % c;
}
return res;
}
signed main()
{
ios_base::sync_with_stdio(0);cin.tie(0);
int n;
cin >> n;
if(n <= 14)
{
vector < int > a(n + 1);
int sum = 0;
for(int i = n;i >= 1;i--)
{
cin >> a[i];
sum += (i * a[i]) % mod;
}
cout << (sum - ((n * (n + 1)) / 2) + 1) % mod << endl;
return 0;
}
vector < int > a(n + 1);
for(int i = n;i >= 1;i--)
{
cin >> a[i];
}
vector < int > dp(n + 1);
dp[1] = 1;
dp[2] = 3;
for(int i = 3;i <= n;i++)
{
dp[i] = (mod_exp(2 , i , mod) - dp[i - 1]) % mod;
}
cout << dp[n] << endl;
}
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