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  1. #include <bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. const int mod = 1e9+7;
  6.  
  7. const int N = 1e5+5;
  8.  
  9. int n;
  10. long long a[N];
  11. long long pref_mul[N];
  12.  
  13. int fastP(int b, int e){
  14.     if(!e)
  15.         return 1;
  16.     if(e & 1)
  17.         return b * 1ll * fastP(b * 1ll * b % mod, e >> 1) % mod;
  18.     return fastP(b * 1ll * b % mod, e >> 1) % mod;
  19. }
  20.  
  21. int main(){
  22.     cin >> n;
  23.     for(int i = 1; i <= n; i++){
  24.         cin >> a[i];
  25.     }
  26.     pref_mul[0] = 1;
  27.     for(int i = 1; i <= n; i++){
  28.         pref_mul[i] = pref_mul[i - 1] * a[i];
  29.         pref_mul[i] %= mod;
  30.     }
  31.     int to = ((n+1)/2) + 1;
  32.     long long sum = 0;
  33.     for(int i = 1; i <= to; i++){
  34.         sum += (pref_mul[i + n/2 - 1] * fastP(pref_mul[i - 1] , mod - 2)) % mod;
  35.         sum %= mod;
  36.     }
  37.     cout << sum << "\n";
  38. }
  39.  
Success #stdin #stdout 0s 4476KB
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https://ideone.com/eIRsPh
language:
C++14 (gcc 8.3)
created:
3 years ago
visibility:
public

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