1 public class Solution {
2 public List<List<String>> findLadders(String beginWord, String endWord, Set<String> wordList) {
3 List<List<String>> res = new LinkedList<List<String>>();
4 Map<String, Integer> visited = new HashMap<>();
5 Queue<Node> queue = new LinkedList<>();
6 List<Node> nodeList = new LinkedList<Node>();
7 visited.put(beginWord, 0);
8 queue.offer(new Node(beginWord));
9 int lastCnt = 1;
10 int currCnt = 0;
11 int level = 1;
12 boolean foundEndWord = false;
13
14 while(!queue.isEmpty()) {
15 Node currNode = queue.poll();
16 StringBuilder wordBuff = new StringBuilder(currNode.word);
17 lastCnt--;
18 for(int i = 0; i < wordBuff.length(); i++) {
19 char currChar = wordBuff.charAt(i);
20 for(char c = 'a'; c <= 'z'; c++) {
21 if(c == currChar) {
22 continue;
23 }
24
25 wordBuff.setCharAt(i, c);
26 String tmpWord = wordBuff.toString();
27 Node tmpNode = new Node(tmpWord, currNode);
28
29 if(endWord.equals(tmpWord)) {
30 nodeList.add(tmpNode);
31 foundEndWord = true;
32 }
33
34 if(wordList.contains(tmpWord)) {
35 if(visited.containsKey(tmpWord) && visited.get(tmpWord)<level) {
36 continue;
37 }
38 currCnt++;
39 queue.offer(tmpNode);
40 visited.put(tmpWord, level);
41 }
42 }
43 wordBuff.setCharAt(i, currChar);
44 }
45
46 if(lastCnt == 0) {
47 if(foundEndWord) {
48 break;
49 }
50 lastCnt = currCnt;
51 currCnt = 0;
52 level++;
53 }
54 }
55
56 for(Node currNode: nodeList) {
57 List<String> list = new LinkedList<>();
58 list.add(currNode.word);
59 while(currNode.parent != null) {
60 list.add(0, currNode.parent.word);
61 currNode = currNode.parent;
62 }
63 res.add(list);
64 }
65
66 return res;
67 }
68
69 class Node {
70 Node parent;
71 String word;
72
73 public Node(String word){
74 this.word = word;
75 }
76
77 public Node(String word, Node parent) {
78 this.word = word;
79 this.parent = parent;
80 }
81 }
82 }
