[leetcode] @python 115. Distinct Subsequences

题目链接

https://leetcode.com/problems/distinct-subsequences/

题目原文

Given a string S and a string T, count the number of distinct subsequences of T in S.

A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ACE" is a subsequence of "ABCDE" while "AEC" is not).

Here is an example:
S = "rabbbit", T = "rabbit"

Return 3.

题目大意

给定字符串S和T，判断S中有多少个不同的子串T

解题思路

动态规划求解

代码

class Solution(object):
    def numDistinct(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: int
        """
        dp = [[0 for i in range(len(t) + 1)] for j in range(len(s) + 1)]
        for j in range(len(s) + 1):
            dp[j][0] = 1
        for i in range(1, len(s) + 1):
            for j in range(1, min(i + 1, len(t) + 1)):
                if s[i - 1] == t[j - 1]:
                    dp[i][j] = dp[i - 1][j] + dp[i - 1][j - 1]
                else:
                    dp[i][j] = dp[i - 1][j]
        return dp[len(s)][len(t)]