题目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.

public class WordDictionary {
    static class TrieNode{
        boolean isLeaf;
        Map<Character,TrieNode> content;
        TrieNode(){
            content = new HashMap<Character,TrieNode>();
        }
    }
    
    private TrieNode root;

    public WordDictionary() {
        root = new TrieNode();
    }

    // Adds a word into the data structure.
    public void addWord(String word) {
        if(word == null || word.length() == 0){
            return;
        }
        
        TrieNode node = root;
        TrieNode tempNode = null;;
        for(int i=0, len=word.length(); i<len; i++){
            Character c = word.charAt(i);
            tempNode = node.content.get(c);
            if(tempNode == null){
                tempNode = new TrieNode();
                node.content.put(c,tempNode);
            }
            node = tempNode;
        }
        node.isLeaf = 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(0,word,root);
    }
    
    private boolean search(int idx, String word, TrieNode root){
        if(word == null || word.length() == 0){
            return false;
        }
        
        TrieNode node = root;
        TrieNode tempNode = null;
        for(int i=idx, len=word.length(); i<len; i++){
            Character c = word.charAt(i);
            if('.' == c){
                Map<Character,TrieNode> map = node.content;
                Set<Character> keys = map.keySet();
                boolean result = false;
                for(Character ch : keys){
                    TrieNode trieNode = map.get(ch);
                    if((i == (len-1)) && trieNode.isLeaf){
                        return true;
                    }
                    
                    if(i >= len){
                        return false;
                    }
                    result = result || search(i+1,word,map.get(ch));
                }
                return result;
            }else{
                tempNode = node.content.get(c);
                if(tempNode == null){
                    return false;
                }
                node = tempNode;
            }
        }
        return node.isLeaf;
    }
}

// Your WordDictionary object will be instantiated and called as such:
// WordDictionary wordDictionary = new WordDictionary();
// wordDictionary.addWord("word");
// wordDictionary.search("pattern");