poj 2096 (概率DP入门)

http://poj.org/problem?id=2096

 

概率DP:

 

#include<iostream>
#include<cstdio>
using namespace std;
double dp[1003][1003];
int main()
{
    int n,s,i,j;
    cin>>n>>s;
    for (i=n;i>=0;i--)
    {
        for (j=s;j>=0;j--)
        {
            if (i==n&&j==s) continue;
            dp[i][j]=(n*s+(n-i)*j*dp[i+1][j]+dp[i][j+1]*i*(s-j)+dp[i+1][j+1]*(n-i)*(s-j))/(n*s-i*j);
        }
    }
    printf("%0.4lf\n",dp[0][0]);
}

#include<iostream>
#include<cstdio>
using namespace std;
double dp[1003][1003];
int main()
{
    int n,s,i,j;
    cin>>n>>s;
    for (i=n;i>=0;i--)
    {
        for (j=s;j>=0;j--)
        {
            if (i==n&&j==s) continue;
            dp[i][j]=(n*s+(n-i)*j*dp[i+1][j]+dp[i][j+1]*i*(s-j)+dp[i+1][j+1]*(n-i)*(s-j))/(n*s-i*j);
        }
    }
    printf("%0.4lf\n",dp[0][0]);
}