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