Edit Distance

Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)

You have the following 3 operations permitted on a word:

a) Insert a character
b) Delete a character
c) Replace a character

public class Solution {
    public int minDistance(String word1, String word2) {
        int len1 = word1 == null ? 0 : word1.length();
        int len2 = word2 == null ? 0 : word2.length();
        if(len1 == 0) return len2;
        if(len2 == 0) return len1;
        int[][] map = new int[len1 + 1][len2 + 1];
        for(int i = 0; i <= len1; i ++)
            map[i][0] = i;
        for(int i = 0; i <= len2; i ++)
            map[0][i] = i;
        for(int i = 1; i <= len1; i ++){
            for(int j = 1; j <= len2; j ++){
                map[i][j] = Math.min(Math.min(map[i - 1][j], map[i][j - 1]) + 1, 
                                     map[i - 1][j - 1] + (word1.charAt(i - 1) == word2.charAt(j - 1) ? 0 : 1));
            }
        }
        return map[len1][len2];
    }
}