Delete Operation for Two Strings LeetCode solution in Python

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class Solution:
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    def minDistance(self, word1: str, word2: str) -> int:
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        m = len(word1)
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        n = len(word2)
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        a = []
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        for i in range(m + 1):
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            a.append([])
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            for j in range(n + 1):
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                a[-1].append(0)
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        for i in range(m):
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            for j in range(n):
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                if word1[i] == word2[j]:
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                    a[i + 1][j + 1] = 1 + a[i][j]
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                else:
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                    a[i + 1][j + 1] = max(a[i][j + 1], a[i + 1][j])
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        return m + n - (2 * a[-1][-1])