Interleaving String — 2D DP

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