leetcode hard模式专杀之72. Edit Distance

这题之所以能成为hard模式，是因为在删，插，换这三个合法动作的前提下，要考虑周全递归条件，才能写出递归表达式，才能用动态规划，老实说这个过程不容易，这个表达式看起来长得就像个错误的答案，但是就是能work，上代码：

public class Solution {
    public int minDistance(String word1, String word2) {
        int row = word1.length() + 1;
        int col = word2.length() + 1;

        int[][] f = new int[row][col];

        for (int i = 0; i < row; i++)
            f[i][0] = i;

        for (int i = 0; i < col; i++)
            f[0][i] = i;

        for (int i = 1; i < row; i++)
            for (int j = 1; j < col; j++){
                if (word1.charAt(i-1) == word2.charAt(j-1)){
                    f[i][j] = f[i-1][j-1];
                }
                else{
                    f[i][j] = f[i-1][j-1] + 1;
                }

                f[i][j] = Math.min(f[i][j], Math.min(f[i-1][j]+1, f[i][j-1]+1));
            }

        return f[row-1][col-1];
    }
}