BZOJ 4008 [HNOI2015] 亚瑟王

期望DP
详情见黄学长博客

#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <algorithm>
#include <cstring>
using namespace std ;
const int T=450;
const int N=230;
const int R=150;

int t,n,r;
double p[N],f[N][N],pw[N][N];
int d[N];
void init (){
    cin >>t;
}
void readin (){
    scanf ("%d %d",&n,&r);
    int i;
    for (i=1;i<=n;i++){
        scanf ("%lf %d",&p[i],&d[i]);
    }
}
void work (){
    int i,j;
    double ans=0;
    memset (f,0,sizeof (f));
    memset (pw,0,sizeof (pw));
    for (i=1;i<=n;i++){
        pw[i][0]=1;
        for (j=1;j<=r;j++) pw[i][j]=pw[i][j-1]*(1-p[i]);
    }
    f[0][r]=1;
    for (i=1;i<=n;i++){
        for (j=0;j<=r;j++){
            f[i][j]+=f[i-1][j]*pw[i][j];
            if (j>=1){
                f[i][j-1]+=f[i-1][j]*(1-pw[i][j]);
                ans+=f[i-1][j]*(1-pw[i][j])*d[i];
            }
        }
    }
    printf ("%.10lf\n",ans);
}
int main (){
    init ();
    int i;
    for (i=1;i<=t;i++){
        readin ();
        work ();
    }
    return 0;
}