Dice Possibility

What is possibility of rolling N dice and the sum of the numbers equals to M?

Input

Two integers N and M. (1 ≤ N ≤ 100, 1 ≤ M ≤ 600)

Output

Output the possibility in percentage with 2 decimal places.

Sample Input

2 10

Sample Output

8.33

题意: n 个骰子掷出 m 点的概率
简单概率dp

#include <iostream>
#include <stdio.h>
using namespace std;

double dp[105][605]; //i 个骰子掷出 j 的情况

void Init()
{
    dp[0][0]=1;
    for (int i=1;i<=100;i++)
    {
        for (int j=i*1;j<=i*6;j++)
        {
            for (int k=1;k<=6;k++)
                if (j-k>=0)
                    dp[i][j]+=dp[i-1][j-k]*1.0/6;
        }
    }
}

int main()
{
    Init();
    int n,m;
    while (scanf("%d%d",&n,&m)!=EOF)
    {
        printf("%.2lf
",dp[n][m]*100);
    }
    return 0;
}