实现前缀树(增、判断是否有该单词，是否有该前缀)

//Implement Trie (Prefix Tree)
//Implement a trie with insert, search, and startsWith methods.
//You may assume that all inputs are consist of lowercase letters a-z.
class MYTrieNode {
    char val;
    boolean isWord;
    MYTrieNode[] subNodes = new  MYTrieNode[26];
    MYTrieNode(char val) {
        this.val = val;
    }
}

class Trie {
    private MYTrieNode root;
    /** Initialize your data structure here. */
    public Trie() {
        root = new MYTrieNode(' ');
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        MYTrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            if (node.subNodes[word.charAt(i) - 'a'] != null) {
                node = node.subNodes[word.charAt(i) - 'a'] ;
            } else {
                node.subNodes[word.charAt(i) - 'a'] = new MYTrieNode(word.charAt(i));
                node = node.subNodes[word.charAt(i) - 'a'];
            }
        }
        node.isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        MYTrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            if (node.subNodes[word.charAt(i) - 'a'] != null) {
                node = node.subNodes[word.charAt(i) - 'a'] ;
            } else {
                return false;
            }
        }
        return node.isWord;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        MYTrieNode node = root;
        for (int i = 0; i < prefix.length(); i++) {
            if (node.subNodes[prefix.charAt(i) - 'a'] != null) {
                node = node.subNodes[prefix.charAt(i) - 'a'] ;
            } else {
                return false;
            }
        }
        return true;
    }
}