Leetcode| 392. 判断子序列、115. 不同的子序列 Day55

392. Is Subsequence

dp[i][j] 表示以下标i-1为结尾的字符串s，和以下标j-1为结尾的字符串t，相同子序列的长度为dp[i][j]

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        dp = [[0] * (len(t) + 1) for _ in range((len(s) + 1))]

        for i in range(1, len(s) + 1):
            for j in range(1, len(t) + 1):
                if s[i - 1] == t[j - 1]:
                    dp[i][j] = dp[i - 1][j - 1] + 1
                else:
                    dp[i][j] = dp[i][j - 1]

        if dp[-1][-1] == len(s):
            return True
        return False

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115. Distinct Subsequences

dp[i][j]：以i-1为结尾的s子序列中出现以j-1为结尾的t的个数为dp[i][j]

class Solution:
    def numDistinct(self, s: str, t: str) -> int:
        dp = [[0] * (len(t) + 1) for _ in range((len(s) + 1))]

        for i in range(len(s) + 1):
            dp[i][0] = 1

        for i in range(1, len(s) + 1):
            for j in range(1, len(t) + 1):
                if s[i - 1] == t[j - 1]:
                    dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j]
                else:
                    dp[i][j] = dp[i - 1][j]

        return dp[-1][-1]