Interleaving String

https://leetcode.com/problems/interleaving-string/

class Solution:
    def isInterleave(self, s1: str, s2: str, s3: str) -> bool:
        m = len(s1)
        n = len(s2)
        if m+n != len(s3):
            return False
        dp = [(1+n)*[False] for _ in range(m+1)]
        dp[0][0] = True
        for i in range(1,m+1):
            if s1[i-1] == s3[i-1]:
                dp[i][0] = dp[i-1][0]
        
        for j in range(1,n+1):
            if s2[j-1] == s3[j-1]:
                dp[0][j] = dp[0][j-1]
                
        for i in range(1,m+1):
            for j in range(1,n+1):
                if s1[i-1] == s3[i+j-1] and s2[j-1] != s3[i+j-1]:
                    dp[i][j] = dp[i-1][j]
                
                elif s1[i-1] != s3[i+j-1] and s2[j-1] == s3[i+j-1]:
                    dp[i][j] = dp[i][j-1]
                
                elif s1[i-1] == s3[i+j-1] and s2[j-1] == s3[i+j-1]:
                    dp[i][j] = dp[i][j-1] or dp[i-1][j]
        
        return dp[m][n]