poj 2096 Collecting Bugs 概率dp入门题
2012-10-27 08:54
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e(i,j)=1+(i*j/n/s)e(i,j)(原地不动)+(i*(s-j)/n/s)e(i,j+1)(s-j中发现bug)+((n-i)*j/n/s)e(i+1,j)(n-i中发现bug)+(n-i)(s-j)/n/s*e(i+1,j+1)(s-j和n-i中发现bug)
#include<iostream> #include<cstdio> #include<memory.h> using namespace std; double e[1005][1005]; int main(){ int n,s; while(~scanf("%d%d",&n,&s)){ 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 te=n*s*(1.0); e[i][j]=(1+e[i][j+1]*i*(s-j)/te+e[i+1][j]*(n-i)*j/te+e[i+1][j+1]*(n-i)*(s-j)/te)/(1-i*j/te); } } printf("%.4lf\n",e[0][0]); } }
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