利用动态规划的思想
dp[i][j] = dp[i][j] + dp[i - 1][j - k] (1 <= k <= f)
代码是leetcode的答案，和书上的问题不完全一样

class Solution:
    def numRollsToTarget(self, d: int, f: int, target: int) -> int:
        m = 10**9+7
        res = [[0]*(target+1) for i in range(d+1)]
        res[0][0] = 1
        for i in range(1,d+1):
            for j in range(1,f+1):
                for k in range(j,target+1):
                    res[i][k] = (res[i][k] + res[i - 1][k - j]) % m
        return res[-1][-1]