Solution.java

/**
 * 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) {
        if (word1 == null || word2 == null) {
            return 0;
        }
        if (word1.length() <= 0) {
            return word2.length();
        }
        if (word2.length() <= 0) {
            return word1.length();
        }
        int[][] matrix = new int[word1.length() + 1][word2.length() + 1];
        for (int i = 0; i < word1.length() + 1; i++) {
            matrix[i][0] = i;
        }
        for (int i = 0; i < word2.length() + 1; i++) {
            matrix[0][i] = i;
        }
        for (int i = 1; i < word1.length() + 1; i++) {
            for (int j = 1; j < word2.length() + 1; j++) {
                if (word1.charAt(i - 1) == word2.charAt(j - 1)) {
                    matrix[i][j] = matrix[i - 1][j - 1];
                } else {
                    matrix[i][j] = Math.min(Math.min(matrix[i - 1][j], matrix[i][j - 1]), matrix[i - 1][j - 1]) + 1;
                }
            }
        }
        
        return matrix[word1.length()][word2.length()];
    }
}