Word Ladder II

最新推荐文章于 2022-02-07 22:27:20 发布

转载最新推荐文章于 2022-02-07 22:27:20 发布 · 45 阅读

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原文链接：http://www.cnblogs.com/RazerLu/p/3537175.html

本文详细阐述了如何使用广度优先搜索算法找到从起始单词到目标单词的所有可能路径，涉及图论、数据结构与算法知识。

http://www.cnblogs.com/shawnhue/archive/2013/06/05/leetcode_126.html

http://fisherlei.blogspot.com/2013/02/leetcode-word-ladder-ii-solution.html

http://blog.youkuaiyun.com/niaokedaoren/article/details/8884938

 1 class Node {
 2     int no;
 3     String val;
 4     LinkedList<Node> prev;    
 5     
 6     Node(int no, String v) {
 7         this.no = no;
 8         this.val = v;
 9     }
10     
11     void addPrev(Node pNode) {
12         if (prev == null) {
13             prev = new LinkedList<Node>();
14         }
15         prev.add(pNode);
16     }
17 }
18 
19 public class Solution {    
20     ArrayList<ArrayList<String>> answer;
21     
22     public void findPath(Node node, ArrayList<String> cur, String start) {
23         if (node.val.equals(start)) {
24             answer.add(cur);
25             return;
26         }
27         ArrayList<String> temp;
28         for (Node n : node.prev) {
29             temp = new ArrayList<String>(cur);
30             temp.add(0, n.val);
31             findPath(n, temp, start);
32         }
33     }
34     
35     public ArrayList<ArrayList<String>> findLadders(String start, String end, HashSet<String> dict) {
36         // Start typing your Java solution below
37         // DO NOT write main() function
38         HashMap<String, Node> map = new HashMap<String, Node>();
39         Queue<Node> queue = new LinkedList<Node>();
40         Node node = new Node(0, start);
41         Node endNode = null;
42         map.put(start, node);
43         queue.add(node);
44         boolean stop = false;
45         while (queue.size() > 0 && !stop) {
46             int count = queue.size();
47             for (int i = 0; i < count; i++) {
48                 node = queue.poll();
49                 for (int j = 0; j < node.val.length(); j++) {
50                     StringBuilder t = new StringBuilder(node.val);
51                     for (char k = 'a'; k <= 'z'; k++) {
52                         t.setCharAt(j, k);
53                         if (dict.contains(t.toString())) {
54                             Node v = map.get(t.toString());
55                             if (v == null) {
56                                 Node temp = new Node(node.no + 1, t.toString());
57                                 temp.addPrev(node);
58                                 queue.add(temp);
59                                 map.put(t.toString(), temp);
60                                 if (t.toString().equals(end)) {
61                                     endNode = temp;
62                                     stop = true;
63                                 }
64                             }
65                             else {
66                                 if (v.no == node.no + 1) {
67                                     v.addPrev(node);
68                                 }
69                             }
70                         }
71                     }
72                 }
73             }
74         }
75         answer = new ArrayList<ArrayList<String>>();
76         if (endNode != null) {
77             findPath(endNode, new ArrayList<String>(Arrays.asList(end)), start);
78         }
79         return answer;
80     }
81 }