211. Add and Search Word - Data structure design.java

Design a data structure that supports the following two operations:
 void addWord(word)
 boolean search(word)
search(word) can search a literal word or a regular expression string containing only letters a-z or'.'means it can represent any one letter.
addWord("bad")
addWord("dad")
addWord("mad")
search("pad") -> false
search("bad") -> true
search(".ad") -> true
search("b..") -> true
   
//此题类似trie的实现，唯一在于点‘.’的处理。因为它可以代表任意字符，因此涉及到DFS处理
   class TrieNode{
    TrieNode[] children;
    boolean isWord;
    public TrieNode(){
       children = new TrieNode[26];
       isWord = false;
    }
}

public class WordDictionary {
    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 node = root;
        for(int i = 0; i < word.length(); i++){
            int index = word.charAt(i) - 'a';
            if(node.children[index] == null){
                node.children[index] = new TrieNode();
            }
            node = node.children[index];
        }
        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 match(word.toCharArray(), 0, root);
    }
    
    public boolean match(char[] chs, int i, TrieNode node){ //从node往下找，匹配chs的从第i开始的字符
        if(i == chs.length){
            return node.isWord;
        }
        if(chs[i] != '.'){ //普通字母，返回 树中当前字母存在 && 从下一个下标找，从这个字母节点往下找，都匹配
            return node.children[chs[i] - 'a'] != null && match(chs, i + 1, node.children[chs[i] - 'a']);
        }else{ //如果是"."，看树中上一个node的所有children中，哪个字母是存在的，且这个字母之后的所有都匹配，只要找到一个就可以返回true
            for(int j = 0; j < 26; j++){
                if(node.children[j] != null && match(chs, i + 1, node.children[j])){
                    return true;
                }
            }
        }
        return false;
    }
}