HDU-4336

概率DP

    

#include <cstdio>#include <cstring>#define _cle(m, a) memset(m, a, sizeof(m))#define N (1<<20)double dp[N + 1];double p[25];int main(){    int n;    double t;    while(~scanf("%d", &n))    {        _cle(dp, 0);        for(int i = 0; i < n; i++)            scanf("%lf", &p[i]);        for(int i = (1<<n) - 2; i >= 0; i--)        {            t = 0.0;            dp[i] ++;            for(int j = 0; j < n; j++)                if(!(i & (1<<j)))                {                    dp[i] += dp[i | (1<<j)] * p[j];                    t += p[j];                }            dp[i] /= t;        }        printf("%.4lf\n", dp[0]);    }    return 0;}