解题思路：

动态规划

class Solution {public int minDistance(String word1, String word2) {int n1 = word1.length();int n2 = word2.length();int[][] dp = new int[n1 + 1][n2 + 1];for (int j = 1; j <= n2; j++) dp[0][j] = dp[0][j - 1] + 1;for (int i = 1; i <= n1; i++) dp[i][0] = dp[i - 1][0] + 1;for (int i = 1; i <= n1; i++) {for (int j = 1; j <= n2; j++) {if (word1.charAt(i - 1) == word2.charAt(j - 1)) dp[i][j] = dp[i - 1][j - 1];else dp[i][j] = Math.min(Math.min(dp[i - 1][j - 1], dp[i][j - 1]), dp[i - 1][j]) + 1;}}return dp[n1][n2];}
}