public class WordDictionary {
    class TrieNode {
        TrieNode[] children;
        int count;
        TrieNode() {
            count = 0;
            children = new TrieNode[26];
        }
    }
    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;
        int i = 0;
        while (i < word.length()) {
            if (cur.children[word.charAt(i) - ‘a‘] == null) {
                cur.children[word.charAt(i) - ‘a‘] = new TrieNode();
            }
            cur = cur.children[word.charAt(i) - ‘a‘];
            i++;
        }
        cur.count++;
    }
    
    /** 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 searchHelper(word, 0, root);
    }
    
    public boolean searchHelper(String word, int start, TrieNode node) {
        // node != null
        int i = start;
        TrieNode cur = node;
        while (i < word.length() && word.charAt(i) != ‘.‘) {
            if (cur.children[word.charAt(i) - ‘a‘] == null) {
                return false;
            }
            cur = cur.children[word.charAt(i) - ‘a‘];
            i++;
        }
        // didn‘t meet ‘.‘
        if (i == word.length()) {
            if (cur.count == 0) {
                return false;
            } else {
                return true;   
            }
        }
        // meet ‘.‘
        for (int j = 0; j < 26; j++) {
            if (cur.children[j] != null && searchHelper(word, i + 1, cur.children[j])) {
                return true;
            }
        }
        return false;
    }
}

/**
 * Your WordDictionary object will be instantiated and called as such:
 * WordDictionary obj = new WordDictionary();
 * obj.addWord(word);
 * boolean param_2 = obj.search(word);
 */