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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3.  
  4. //defines
  5. #define openin freopen("input.txt","r",stdin)
  6. #define openout freopen("output.txt","w",stdout)
  7. #define fast ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
  8. #define ll long long
  9. #define int long long
  10. #define mod 1000000007
  11. #define rep(i,x,y) for (__typeof(x) i=x;(x<=y?i<=y:i>=y);i=(x<=y?i+1:i-1))
  12. #define all(c) (c).begin(),(c).end()
  13. #define ff first
  14. #define ss second
  15. #define pb push_back
  16. #define mp make_pair
  17. int n ;
  18. int arr[1000006] ;
  19. int p[1000006] ;
  20. int32_t main()
  21. {
  22.     fast;
  23.     cin >> n ;
  24.     rep(i,1,n) cin >> arr[i] ;
  25.     p[0] = 1ll ;
  26.     rep(i,1,1000000)
  27.     {
  28.         p[i] = p[i-1]*2ll ;
  29.         p[i] %= mod ;
  30.     }
  31.     int ans = 0 ;
  32.     for(int k = 1 ; k <= n/2 ; k++ )
  33.     {
  34.         int temp = p[n] + p[n-1] - p[n-k] - p[k-1] ;
  35.         temp %= mod ;
  36.         int temp2 = arr[k] + arr[n+1-k] ;
  37.         temp2 %= mod ;
  38.         temp = (temp * temp2) ;
  39.         temp %= mod ;
  40.         ans += temp ;
  41.         ans %= mod ;
  42.     }
  43.     if(n%2)
  44.     {
  45.         int i = (n+1)/2 ;
  46.         int temp = p[n] + p[n-1] - p[n-i] - p[i-1] ;
  47.         temp %= mod ;
  48.         temp *= arr[i] ;
  49.         temp %= mod ;
  50.         ans += temp ;
  51.         ans %= mod ;
  52.     }
  53.     cout << ans << '\n' ;
  54.     return 0;
  55. }
  56.  
Success #stdin #stdout 0.01s 19088KB
comments (?)
stdin 
3
1 3 6
stdout 
73
https://ideone.com/pXfyU8
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
secret

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