97. 交错字符串

 

class Solution:
    def isInterleave(self, s1: str, s2: str, s3: str) -> bool:

        len1=len(s1)
        len2=len(s2)
        len3=len(s3)

        if (len1+len2 != len3):
            return False

        dp=[[False]*(len2+1) for i in range(len1+1)]
        dp[0][0]=True

        for i in range(1, len1+1):
            dp[i][0]=(dp[i-1][0] and s1[i-1]==s3[i-1])

        for i in range(1, len2+1):
            dp[0][i]=(dp[0][i-1] and s2[i-1]==s3[i-1])

        for i in range(1, len1+1):
            for j in range(1, len2+1):
                dp[i][j]=(dp[i][j-1] and s2[j-1]==s3[i+j-1]) or (dp[i-1][j] and s1[i-1]==s3[i+j-1])

        return dp[-1][-1]