LeetCode: Edit Distance

LeetCode: Edit Distance 

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/**
 * Description: 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.)
 * <p/>
 * You have the following 3 operations permitted on a word:
 * <p/>
 * a) Insert a character
 * <p/>
 * b) Delete a character
 * <p/>
 * c) Replace a character
 *
 * @author hzhou
 */
 public class EditDistance {
     public int minDistance(String word1, String word2) {
         if (word1 == null && word2 == null) {
             return 0;
         }
         if (word1 == null || word1.isEmpty()) {
             return word2.length();
         }
         if (word2 == null || word2.isEmpty()) {
             return word1.length();
         }
         int[][] map = new int[word1.length() + 1][word2.length() + 1];
         for (int i = 0; i <= word1.length(); i++) {
             map[i][0] = i;
         }
         for (int i = 0; i <= word2.length(); i++) {
             map[0][i] = i;
         }
         for (int i = 0; i < word1.length(); i++) {
             char c1 = word1.charAt(i);
             for (int j = 0; j < word2.length(); j++) {
                 char c2 = word2.charAt(j);
                 if (c1 == c2) {
                     map[i + 1][j + 1] = map[i][j];
                 } else {
                     int r1 = map[i][j + 1] + 1;
                     int r2 = map[i][j] + 1;
                     int r3 = map[i + 1][j] + 1;
                     map[i + 1][j + 1] = Math.min(r1, Math.min(r2, r3));
                 }
             }
         }
         return map[word1.length()][word2.length()];
     }
 }