Leetcode: Add and Search Word - Data structure design

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.

 1 public class WordDictionary {
 2     public class TrieNode {
 3         int num; //count how many words go through this TrieNode
 4         TrieNode[] sons; //Arrays of children
 5         boolean isEnd;
 6         char val;
 7         
 8         public TrieNode() {
 9             this.num = 0;
10             this.sons = new TrieNode[26];
11             this.isEnd = false;
12         }
13     }
14     
15     TrieNode root;
16     
17     public WordDictionary() {
18         this.root = new TrieNode();
19     }
20 
21     // Adds a word into the data structure.
22     public void addWord(String word) {
23         if (word==null || word.length()==0) return;
24         char[] arr = word.toCharArray();
25         TrieNode node = this.root;
26         for (char c : arr) {
27             int pos = (int)(c - ‘a‘);
28             if (node.sons[pos] == null) {
29                 node.sons[pos] = new TrieNode();
30                 node.sons[pos].num = 1;
31                 node.sons[pos].val = c;
32             }
33             else {
34                 node.sons[pos].num++;
35             }
36             node = node.sons[pos];
37         }
38         node.isEnd = true;
39     }
40 
41     // Returns if the word is in the data structure. A word could
42     // contain the dot character ‘.‘ to represent any one letter.
43     public boolean search(String word) {
44         int len = word.length();
45         TrieNode node = this.root;
46         return search(word, node, 0, len);
47     }
48     
49     public boolean search(String word, TrieNode node, int cur, int len) {
50         if (cur == len) return node.isEnd;
51         char w = word.charAt(cur);
52         if (w == ‘.‘) {
53             for (int j=0; j<26; j++) {
54                 if (node.sons[j] != null) {
55                     if (search(word, node.sons[j], cur+1, len))
56                         return true;
57                 }
58             }
59             return false;
60         }
61         else {
62             int pos = (int)(w - ‘a‘);
63             if (node.sons[pos] == null) return false;
64             return search(word, node.sons[pos], cur+1, len);
65         }
66     }
67 }
68 
69 // Your WordDictionary object will be instantiated and called as such:
70 // WordDictionary wordDictionary = new WordDictionary();
71 // wordDictionary.addWord("word");
72 // wordDictionary.search("pattern");