[概率dp] hdu 4336 Card Collector

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代码

#include<iostream>#include<cstdio>#include<cstring>#include<string>#include<cmath>#include<map>#include<algorithm>using namespace std;const double eps=1e-9;const int maxn=20;const int maxs=(1<<maxn)+5;double p[maxn],dp[maxs];int num[maxs]={0};int n;int main(){    for(int i=0;i<(1<<20);i++)        {            int x=i;            while(x>0)            {                num[i]+=(x&1);                x>>=1;            }        }    while(cin>>n)    {        p[0]=1;        for(int i=1;i<=n;i++) scanf("%lf",&p[i]),p[0]-=p[i];        dp[(1<<n)-1]=0;        for(int len=n-1;len>=0;len--)        {            for(int s=0;s<(1<<n);s++)            {                if(num[s]!=len) continue;                double  x=p[0],y=1.0;                for(int dig=0;dig<n;dig++)                    if((s>>dig)&1)                        x+=p[dig+1];                    else                        y+=p[dig+1]*dp[(s^(1<<dig))];                x=1-x;                if(fabs(x)<eps) {dp[s]=0;continue;}                dp[s]=y/x;            }        }        printf("%.9f\n",dp[0]);    }    return 0;}

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