poj 2096 (概率DP)

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 double dp[1003][1003];
 5 int main()
 6 {
 7     int n,s,i,j;
 8     cin>>n>>s;
 9     for (i=n;i>=0;i--)
10     {
11         for (j=s;j>=0;j--)
12         {
13             if (i==n&&j==s) continue;
14             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);
15         }
16     }
17     printf("%0.4lf\n",dp[0][0]);
18 }

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 double dp[1003][1003];
 5 int main()
 6 {
 7     int n,s,i,j;
 8     cin>>n>>s;
 9     for (i=n;i>=0;i--)
10     {
11         for (j=s;j>=0;j--)
12         {
13             if (i==n&&j==s) continue;
14             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);
15         }
16     }
17     printf("%0.4lf\n",dp[0][0]);
18 }