hdu 4336 Card Collector

概率+状态dp

#include <CSTDIO>#include <STRING.H>#include <MATH.H>// hdu 4336/**/const int MAXN = 21;int n;double dp[1<<MAXN], p[MAXN];int main()   {#ifndef ONLINE_JUDGE    freopen("in.txt", "r", stdin);#endifint i, j;double pz;// 一张都没有的概率while (scanf("%d", &n) == 1){for (i = 0, pz = 0.0; i < n; ++i)scanf("%lf", &p[i]), pz += p[i];pz = 1 - pz;dp[(1<<n)-1] = 0.0; // 卡片全满int t = 1<<n;double a, b;for (i = t - 2 ; i >= 0; --i){a = 1.0;b = pz;for (j = 0; j<n; ++j){if ( i & (1<<j))b += p[j];elsea += p[j] * dp[i | (1<<j)];}b = 1 - b;dp[i] = a/b;}printf("%.6lf\n", dp[0]);}return 0;}