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

 class WordDictionary {
private TrieNode root; /** Initialize your data structure here. */
public WordDictionary() {
root = new TrieNode();
} /** Adds a word into the data structure. */
public void addWord(String word) {
TrieNode cur = root;
for (char c: word.toCharArray()) {
if (cur.children[c - 'a'] == null) {
cur.children[c - 'a'] = new TrieNode();
}
cur = cur.children[c - 'a'];
}
cur.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) {
return helper(word, root, 0);
} private boolean helper(String word, TrieNode root, int level) {
if (level == word.length()) {
return root.isWord;
}
char cur = word.charAt(level);
if (cur == '.') {
for (TrieNode child : root.children) {
if (child != null && helper(word, child, level + 1)) {
return true;
}
}
return false;
} else {
return root.children[cur - 'a'] != null && helper(word, root.children[cur - 'a'], level + 1);
}
}
} class TrieNode {
TrieNode[] children;
boolean isWord; public TrieNode() {
children = new TrieNode[26];
isWord = false;
}
} /**
* Your WordDictionary object will be instantiated and called as such:
* WordDictionary obj = new WordDictionary();
* obj.addWord(word);
* boolean param_2 = obj.search(word);
*/

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