Card Collector

Aimee

转态转移非常好想

状态压缩一下。然后倒着转移

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
double dp[1<<21];
int n;
double p[21];
double fai=1;
int main(){
	while(~scanf("%d",&n)){
		fai=1;
		memset(dp,0,sizeof(dp));
		for(int i=1;i<=n;++i){
			scanf("%lf",&p[i]);
			fai-=p[i];
		}
		for(int i=(1<<n)-2;i>=0;--i){
			double x=0;
			double y=fai;
			for(int j=1;j<=n;++j){
				if((i&(1<<(j-1)))){
					y+=p[j];
				}else{
					
					x+=p[j]*(1+dp[i|(1<<(j-1))]);
				}
			}
			dp[i]=(x+y)/(1-y);
		}
		printf("%.4lf\n",dp[0]);
	}
	return 0;
}