[LC] 211. Add and Search Word

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.

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

 1 class WordDictionary {
 2     private TrieNode root;
 3 
 4     /** Initialize your data structure here. */
 5     public WordDictionary() {
 6         root = new TrieNode(); 
 7     }
 8     
 9     /** Adds a word into the data structure. */
10     public void addWord(String word) {
11         TrieNode cur = root;
12         for (char c: word.toCharArray()) {
13             if (cur.children[c - 'a'] == null) {
14                 cur.children[c - 'a'] = new TrieNode();
15             }
16             cur = cur.children[c - 'a'];
17         }
18         cur.isWord = true;
19     }
20     
21     /** Returns if the word is in the data structure. A word could contain the dot character '.' to represent any one letter. */
22     public boolean search(String word) {
23         return helper(word, root, 0);
24     }
25     
26     private boolean helper(String word, TrieNode root, int level) {
27         if (level == word.length()) {
28             return root.isWord;
29         }
30         char cur = word.charAt(level);
31         if (cur == '.') {
32             for (TrieNode child : root.children) {
33                 if (child != null && helper(word, child, level + 1)) {
34                     return true;
35                 }
36             }
37             return false;
38         } else {
39             return root.children[cur - 'a'] != null && helper(word, root.children[cur - 'a'], level + 1);
40         }
41     }
42 }
43 
44 class TrieNode {
45     TrieNode[] children;
46     boolean isWord;
47     
48     public TrieNode() {   
49         children = new TrieNode[26];
50         isWord = false;
51     }
52 }
53 
54 /**
55  * Your WordDictionary object will be instantiated and called as such:
56  * WordDictionary obj = new WordDictionary();
57  * obj.addWord(word);
58  * boolean param_2 = obj.search(word);
59  */