题目：
Design a data structure that supports the following two operations:
void addWord(word) bool search(word)
search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.
For example:
addWord("bad")
addWord("dad")
addWord("mad")
search("pad") -> false
search("bad") -> true
search(".ad") -> true
search("b..") -> true
Note:
You may assume that all words are consist of lowercase letters a-z.
链接： http://leetcode.com/problems/add-and-search-word-data-structure-design/
题解：
设计一个Data Structure来search和add单词。这道题我们又可以用一个R-Way Trie来完成。 像JQuery里面的Auto-complete功能其实就可以用R-Way Trie based method来设计和编程。注意当字符为"."的时候我们要loop当前节点的全部26个子节点，这里要用一个DFS。
Time Complexity - O(n)， Space Complextiy - O(26n)。
public class WordDictionary { private TrieNode root = new TrieNode(); private class TrieNode { private final int R = 26; // radix = 26 public TrieNode[] next; public boolean isWord; public TrieNode() { next = new TrieNode[R]; } } // Adds a word into the data structure. public void addWord(String word) { if(word == null || word.length() == 0) return; TrieNode node = root; int d = 0; while(d < word.length()) { char c = word.charAt(d); if(node.next[c - ‘a‘] == null) node.next[c - ‘a‘] = new TrieNode(); node = node.next[c - ‘a‘]; d++; } node.isWord = true; } // Returns if the word is in the data structure. A word could // contain the dot character ‘.‘ to represent any one letter. public boolean search(String word) { if(word == null || word.length() == 0) return false; TrieNode node = root; int d = 0; return search(node, word, 0); } private boolean search(TrieNode node, String word, int d) { if(node == null) return false; if(d == word.length()) return node.isWord; char c = word.charAt(d); if(c == ‘.‘) { for(TrieNode child : node.next) { if(child != null && search(child, word, d + 1)) return true; } return false; } else { return search(node.next[c - ‘a‘], word, d + 1); } } } // Your WordDictionary object will be instantiated and called as such: // WordDictionary wordDictionary = new WordDictionary(); // wordDictionary.addWord("word"); // wordDictionary.search("pattern");
Reference:
https://leetcode.com/discuss/35878/java-hashmap-backed-trie
https://leetcode.com/discuss/35928/my-simple-and-clean-java-code
211. Add and Search Word - Data structure design
原文：http://www.cnblogs.com/yrbbest/p/4979621.html