def minDistance(self, word1: str, word2: str) -> int:
    n = len(word1)
    m = len(word2)

    # ----求最长公共子序列LCS（Longest Common Subsequence）的长度
    dp = [[0 for _ in range(m + 1)] for _ in range(n + 1)]  # 虚指
    for i in range(1, n + 1):
        for j in range(1, m + 1):
            if word1[i - 1] == word2[j - 1]:  # 转成实指
                dp[i][j] = dp[i - 1][j - 1] + 1
            else:
                dp[i][j] = max(dp[i - 1][j], dp[i][j - 1])
    LCSn = dp[n][m]
    return (n - LCSn) + (m - LCSn)