题目：

题解：

class Solution:def numDistinct(self, s: str, t: str) -> int:m, n = len(s), len(t)if m < n:return 0dp = [[0] * (n + 1) for _ in range(m + 1)]for i in range(m + 1):dp[i][n] = 1for i in range(m - 1, -1, -1):for j in range(n - 1, -1, -1):if s[i] == t[j]:dp[i][j] = dp[i + 1][j + 1] + dp[i + 1][j]else:dp[i][j] = dp[i + 1][j]return dp[0][0]