Interleaving String LeetCode solution in Python

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