poj2096 Collecting Bugs----期望复习
#include<iostream>#include<cstdlib>#include<stdio.h>#include<memory.h>using namespace std;double e[1005][1005];int main(){ int n,s; while(scanf("%d%d",&n,&s)!=EOF) { memset(e,0,sizeof(e)); for(int i=n;i>=0;i--) for(int j=s;j>=0;j--) { if(i==n&&j==s) continue; double f=1.0*n*s; double p=1+e[i][j+1]*i*(s-j)/f+e[i+1][j]*(n-i)*j/f+e[i+1][j+1]*(n-i)*(s-j)/f; //cout<<p<<endl; double q=1-i*j/f; //cout<<q<<endl; e[i][j]=p/q; } printf("%.4lf\n",e[0][0]); }}
