[leetcode] 72. Edit Distance

题目

Given two strings word1 and word2, return the minimum number of operations required to convert word1 to word2.

You have the following three operations permitted on a word:

• Insert a character
• Delete a character
• Replace a character

Example 1:

Input: word1 = "horse", word2 = "ros"
Output: 3
Explanation: 
horse -> rorse (replace 'h' with 'r')
rorse -> rose (remove 'r')
rose -> ros (remove 'e')

Example 2:

Input: word1 = "intention", word2 = "execution"
Output: 5
Explanation: 
intention -> inention (remove 't')
inention -> enention (replace 'i' with 'e')
enention -> exention (replace 'n' with 'x')
exention -> exection (replace 'n' with 'c')
exection -> execution (insert 'u')

Constraints:

• 0 <= word1.length, word2.length <= 500
• word1 and word2 consist of lowercase English letters.

思路

动态规划，与583. Delete Operation for Two Strings类似。

代码

python版本：

class Solution:
    def minDistance(self, word1: str, word2: str) -> int:
        dp = [[99999]*(len(word2)+1) for _ in range(len(word1)+1)]
        for i in range(len(dp)):
            for j in range(len(dp[i])):
                if i == 0 or j == 0:
                    dp[i][j] = i+j
                elif word1[i-1] == word2[j-1]:
                    dp[i][j] = dp[i-1][j-1]
                else:
                    dp[i][j] = min(dp[i-1][j], dp[i][j-1], dp[i-1][j-1])+1
        # [print(i) for i in dp]
        return dp[-1][-1]