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  1. // Coins 
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4.  
  5. int main() {
  6.     ios_base::sync_with_stdio(false);
  7.     cin.tie(nullptr);
  8.  
  9.     int N;
  10.     cin >> N;
  11.  
  12.     vector<double> p(N);
  13.     for (int i = 0; i < N; i++) {
  14.         cin >> p[i];
  15.     }
  16.  
  17.  
  18.     vector<double> dp(N + 1, 0.0);
  19.     dp[0] = 1.0; // 0 coins, 0 heads: probability 1
  20.  
  21.     for (int i = 0; i < N; i++) {
  22.  
  23.         for (int j = i + 1; j >= 1; j--) {
  24.  
  25.             dp[j] = dp[j - 1] * p[i] + dp[j] * (1.0 - p[i]);
  26.         }
  27.         // j = 0: no heads means all tails
  28.         dp[0] = dp[0] * (1.0 - p[i]);
  29.     }
  30.  
  31.  
  32.     int threshold = (N + 1) / 2;
  33.     double ans = 0.0;
  34.     for (int j = threshold; j <= N; j++) {
  35.         ans += dp[j];
  36.     }
  37.  
  38.  
  39.     cout << fixed << setprecision(12) << ans << "\n";
  40.  
  41.     return 0;
  42. }
Success #stdin #stdout 0.01s 5320KB
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stdin
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Standard input is empty
stdout
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0.000000000000
https://ideone.com/axuwI5
language:
C++ (gcc 8.3)
created:
18 hours ago
visibility:
public

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