Add and Search

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 lettersa-zor.. 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

class WordDictionary {
    private class TrieNode {
        TrieNode[] children;
        boolean isWord;
        String word;
        private TrieNode() {
            children = new TrieNode[26];
            isWord = false;
            word = "";
        }
    }
    /** Initialize your data structure here. */
    TrieNode root;
    public WordDictionary() {
        root = new TrieNode(); 
    }

    /** Adds a word into the data structure. */
    public void addWord(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            int pos = word.charAt(i) - 'a';
            if (node.children[pos] == null) {
                node.children[pos] = new TrieNode();
            }
            node = node.children[pos];
        }
        node.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 find(word, root, 0);
    }
    public boolean find (String word, TrieNode root, int index) {
        if (index == word.length()) {
            return root.isWord;
        }
        if (word.charAt(index) == '.') {
            for (TrieNode child : root.children) {
                // if (child != null) {
                //     return find(word, child, index+1);
                // }错误原因不详

                if(child!= null && find(word, child, index+1)) {
                    return true;
                }
            }
            return false;

        }else{
            int c = word.charAt(index) - 'a';
            return (root.children[c] != null && find(word, root.children[c], index + 1));
        }

    }
}

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