Edit Distance

LeetCode 72 · View on LeetCode

Classic 2D DP. dp[i][j] is the minimum edits to convert word1[:i] to word2[:j]. If characters match, no edit needed; otherwise take the min of insert, delete, or replace (all +1).

def min_distance(word1: str, word2: str) -> int:
    m, n = len(word1), len(word2)
    dp = list(range(n + 1))
    for i in range(1, m + 1):
        prev = dp[0]
        dp[0] = i
        for j in range(1, n + 1):
            temp = dp[j]
            if word1[i-1] == word2[j-1]:
                dp[j] = prev
            else:
                dp[j] = 1 + min(prev, dp[j], dp[j-1])
            prev = temp
    return dp[n]

if __name__ == '__main__':
    print(min_distance("horse", "ros"))       # 3
    print(min_distance("intention", "execution"))  # 5
    print(min_distance("", "abc"))            # 3