72. 编辑距离

给你两个单词 word1 和 word2，请你计算出将 word1 转换成 word2 所使用的最少操作数 。

你可以对一个单词进行如下三种操作：

插入一个字符
删除一个字符
替换一个字符

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/edit-distance
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

import java.util.Scanner;

class Solution {
    public static int minDistance(String word1, String word2) {
        if (word1 == null && word2 == null) {
            return 0;
        }

        if (word1 == null) {
            return word2.length();
        }

        if (word2 == null) {
            return word1.length();
        }

        int insert = 1, delete = 1, replace = 1;

        if (replace > insert + delete) {
            replace = insert + delete;
        }

        int[][] dp = new int[word1.length() + 1][word2.length() + 1];

        for (int i = 0; i <= word2.length(); ++i) {
            dp[0][i] = i * insert;
        }

        for (int i = 0; i <= word1.length(); ++i) {
            dp[i][0] = i * delete;
        }

        for (int i = 1; i <= word1.length(); ++i) {
            for (int j = 1; j <= word2.length(); ++j) {
                if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
                    dp[i][j] = dp[i - 1][j - 1];
                } else {
                    dp[i][j] = Math.min(dp[i - 1][j - 1] + replace, Math.min(dp[i][j - 1] + insert, dp[i - 1][j] + delete));
                }
            }
        }

        return dp[word1.length()][word2.length()];
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            System.out.println(minDistance(in.next(), in.next()));
        }
    }
}