Word Ladder II leetcode java
题目:
Given two words (start and end), and a dictionary, find all shortest transformation sequence(s) from start to end, such that:
- Only one letter can be changed at a time
- Each intermediate word must exist in the dictionary
For example,
Given:
start = "hit"
end = "cog"
dict = ["hot","dot","dog","lot","log"]
Return
[
["hit","hot","dot","dog","cog"],
["hit","hot","lot","log","cog"]
]
Note:
- All words have the same length.
- All words contain only lowercase alphabetic characters.
题解:
答案是http://www.1point3acres.com/bbs/thread-51646-1-1.html 上面
iostreamin写的。
我就直接贴过来就好,这道题多读读代码看明白。
代码:
1 public ArrayList<ArrayList<String>> findLadders(String start, String end, HashSet<String> dict) {
2
3 HashMap<String, HashSet<String>> neighbours = new HashMap<String, HashSet<String>>();
4
5 dict.add(start);
6 dict.add(end);
7
8 // init adjacent graph
9 for(String str : dict){
10 calcNeighbours(neighbours, str, dict);
11 }
12
13 ArrayList<ArrayList<String>> result = new ArrayList<ArrayList<String>>();
14
15 // BFS search queue
16 LinkedList<Node> queue = new LinkedList<Node>();
17 queue.add(new Node(null, start, 1)); //the root has not parent and its level == 1
18
19 // BFS level
20 int previousLevel = 0;
21
22 // mark which nodes have been visited, to break infinite loop
23 HashMap<String, Integer> visited = new HashMap<String, Integer>();
24 while(!queue.isEmpty()){
25 Node n = queue.pollFirst();
26 if(end.equals(n.str)){
27 // fine one path, check its length, if longer than previous path it's valid
28 // otherwise all possible short path have been found, should stop
29 if(previousLevel == 0 || n.level == previousLevel){
30 previousLevel = n.level;
31 findPath(n, result);
32 }else {
33 // all path with length *previousLevel* have been found
34 break;
35 }
36 }else {
37 HashSet<String> set = neighbours.get(n.str);
38
39 if(set == null || set.isEmpty()) continue;
40 // note: I'm not using simple for(String s: set) here. This is to avoid hashset's
41 // current modification exception.
42 ArrayList<String> toRemove = new ArrayList<String>();
43 for (String s : set) {
44
45 // if s has been visited before at a smaller level, there is already a shorter
46 // path from start to s thus we should ignore s so as to break infinite loop; if
47 // on the same level, we still need to put it into queue.
48 if(visited.containsKey(s)){
49 Integer occurLevel = visited.get(s);
50 if(n.level+1 > occurLevel){
51 neighbours.get(s).remove(n.str);
52 toRemove.add(s);
53 continue;
54 }
55 }
56 visited.put(s, n.level+1);
57 queue.add(new Node(n, s, n.level + 1));
58 if(neighbours.containsKey(s))
59 neighbours.get(s).remove(n.str);
60 }
61 for(String s: toRemove){
62 set.remove(s);
63 }
64 }
65 }
66
67 return result;
68 }
69
70 public void findPath(Node n, ArrayList<ArrayList<String>> result){
71 ArrayList<String> path = new ArrayList<String>();
72 Node p = n;
73 while(p != null){
74 path.add(0, p.str);
75 p = p.parent;
76 }
77 result.add(path);
78 }
79
80 /*
81 * complexity: O(26*str.length*dict.size)=O(L*N)
82 */
83 void calcNeighbours(HashMap<String, HashSet<String>> neighbours, String str, HashSet<String> dict) {
84 int length = str.length();
85 char [] chars = str.toCharArray();
86 for (int i = 0; i < length; i++) {
87
88 char old = chars[i];
89 for (char c = 'a'; c <= 'z'; c++) {
90
91 if (c == old) continue;
92 chars[i] = c;
93 String newstr = new String(chars);
94
95 if (dict.contains(newstr)) {
96 HashSet<String> set = neighbours.get(str);
97 if (set != null) {
98 set.add(newstr);
99 } else {
HashSet<String> newset = new HashSet<String>();
newset.add(newstr);
neighbours.put(str, newset);
}
}
}
chars[i] = old;
}
}
private class Node {
public Node parent; //previous node
public String str;
public int level;
public Node(Node p, String s, int l){
parent = p;
str = s;
level = l;
}
}
Reference:http://www.1point3acres.com/bbs/thread-51646-1-1.html
Word Ladder II leetcode java的更多相关文章
- Word Break II leetcode java
题目: Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where e ...
- Word Ladder II [leetcode]
本题有几个注意点: 1. 回溯找路径时.依据路径的最大长度控制回溯深度 2. BFS时,在找到end单词后,给当前层做标记find=true,遍历完当前层后结束.不须要遍历下一层了. 3. 能够将字典 ...
- [leetcode]Word Ladder II @ Python
[leetcode]Word Ladder II @ Python 原题地址:http://oj.leetcode.com/problems/word-ladder-ii/ 参考文献:http://b ...
- LeetCode: Word Ladder II 解题报告
Word Ladder II Given two words (start and end), and a dictionary, find all shortest transformation s ...
- [Leetcode Week5]Word Ladder II
Word Ladder II 题解 原创文章,拒绝转载 题目来源:https://leetcode.com/problems/word-ladder-ii/description/ Descripti ...
- 【leetcode】Word Ladder II
Word Ladder II Given two words (start and end), and a dictionary, find all shortest transformation ...
- LeetCode :Word Ladder II My Solution
Word Ladder II Total Accepted: 11755 Total Submissions: 102776My Submissions Given two words (start ...
- leetcode 127. Word Ladder、126. Word Ladder II
127. Word Ladder 这道题使用bfs来解决,每次将满足要求的变换单词加入队列中. wordSet用来记录当前词典中的单词,做一个单词变换生成一个新单词,都需要判断这个单词是否在词典中,不 ...
- 126. Word Ladder II(hard)
126. Word Ladder II 题目 Given two words (beginWord and endWord), and a dictionary's word list, find a ...
随机推荐
- listview重新计算高度
将xml中的ListView改用下面的ListViewForScrollView //ScrollView中嵌入ListView,让ListView全显示出来 public class ListVie ...
- bzoj3111: [Zjoi2013]蚂蚁寻路
题目链接 bzoj3111: [Zjoi2013]蚂蚁寻路 题解 发现走出来的图是一向上的凸起锯齿状 对于每个突出的矩形dp一下就好了 代码 /* */ #include<cstdio> ...
- CF23 E. Tree 树形dp+高精度
题目链接 CF23 E. Tree 题解 CF竟让卡常QAQ dp+高精度 dp[x][j]表示以x为根的子树,x所属的联通块大小为j,的最大乘积(不带j这块 最后f[x]维护以x为根的子树的最大答案 ...
- BZOJ.4816.[SDOI2017]数字表格(莫比乌斯反演)
题目链接 总感觉博客园的\(Markdown\)很..\(gouzhi\),可以看这的. 这个好像简单些啊,只要不犯sb错误 [Update] 真的算反演中比较裸的题了... \(Descriptio ...
- markdown编辑器使用指南
欢迎使用Markdown编辑器写博客 本Markdown编辑器使用StackEdit修改而来,用它写博客,将会带来全新的体验哦: Markdown和扩展Markdown简洁的语法 代码块高亮 图片链接 ...
- Git和Gitlab
参考 http://www.cnblogs.com/clsn/p/7929958.html#auto_id_16https://backlog.com/git-tutorial/cn/intro/in ...
- MySQL 集群
MySQL Galera介绍 主要功能: 同步复制 真正的multi-master,即所有节点可以同时读写数据库 自动的节点成员控制,失效节点自动被清除 新节点加入数据自动复制 真正的并行复制,行级 ...
- POP3_使用SSL链接邮箱并获取邮件
Gmail目前已经启用了POP3和SMTP服务,与其他邮箱不同的是Gmail提供的POP3和SMTP是使用安全套接字层SSL的,因此常规的JavaMail程序是无法收发邮件的,下面是使用JavaMai ...
- CentOS安装openvpn报错:error: route utility is required but missing
centos7特有,直接安装net-tools即可. 参考: https://forums.openvpn.net/viewtopic.php?t=21432
- 面向企业级的开源WebGIS解决方案--MapGuide(对比分析)
在技术特点.功能.架构等方面,MapGuide与其他WebGIS产品有什么区别?本文主要从此角度来介绍MapGuide的特性,以供参考. 本人选择了比较熟悉的几款WebGIS产品:MapServ ...