leetcode--Word Ladder

Given two words (beginWord and endWord), and a dictionary, find the length of shortest transformation sequence from beginWord to endWord, such that:

1. Only one letter can be changed at a time
2. Each intermediate word must exist in the dictionary

For example,

Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]

As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog",
return its length 5.

Note:

• Return 0 if there is no such transformation sequence.
• All words have the same length.
• All words contain only lowercase alphabetic characters.

[java]  view plain  copy

1. public class Solution {  
2.     public int ladderLength(String beginWord, String endWord, Set<String> wordDict) {  
3.         class WordNode{  
4.             String word;  
5.             int step;  
6.             public WordNode(String word, int step) {  
7.                 super();  
8.                 this.word = word;  
9.                 this.step = step;  
10.             }                         
11.         }         
12.         Queue<WordNode> queue = new LinkedList<WordNode>();  
13.         queue.add(new WordNode(beginWord,1));  
14.         wordDict.add(endWord);  
15.         while(!queue.isEmpty()){  
16.             WordNode cur = queue.poll();  
17.             if(cur.word.equals(endWord)){  
18.                 return cur.step;  
19.             }else{  
20.                 char[] arr = cur.word.toCharArray();  
21.                 for(int i=0;i<arr.length;i++){  
22.                     for(int c='a';c<='z';c++){  
23.                         char temp = arr[i];  
24.                         if(c!=temp){  
25.                             arr[i] = (char) c;  
26.                         }  
27.                         String str = new String(arr);  
28.                         if(wordDict.contains(str)){  
29.                             queue.add(new WordNode(str, cur.step+1));  
30.                             wordDict.remove(str);  
31.                         }  
32.                         arr[i] = temp;  
33.                     }  
34.                 }  
35.             }  
36.         }  
37.         return 0;  
38.     }  
39. }  

原文链接http://blog.youkuaiyun.com/crazy__chen/article/details/46523161