Leetcode 211 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.

Solution 1: use Trie will be much easier for string search.

 public class WordDictionary {  
   class TrieNode {  
     private boolean val=false;  
     private TrieNode[] next=new TrieNode[26];  
   }  
   private TrieNode root=new TrieNode();  
   // Adds a word into the data structure.  
   public void addWord(String word) {  
     TrieNode x=root;  
     int i=0;  
     while (i<word.length()) {  
       int index=word.charAt(i++)-'a';  
       if (x.next[index]==null) x.next[index]=new TrieNode();  
       x=x.next[index];  
     }  
     x.val=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) {  
     return search(root,word,0);  
   }  
   private boolean search(TrieNode x, String word, int d) {  
     if (x==null) return false;  
     if (d==word.length()) return x.val;  
     for (int i=0; i<26; i++) {  
       char c=word.charAt(d);  
       if (c=='.' || c=='a'+i) {  
         if (search(x.next[i],word,d+1)) return true;  
       }  
     }  
     return false;  
   }  
 }