leetcode208.实现tire

class Trie {
    public class TrieNode{
        boolean isWord;
        TrieNode[] letters = new TrieNode[26];
    }

    TrieNode root ;
    public Trie() {
        root = new TrieNode();
    }
    /** Inserts a word into the trie. */
    public void insert(String word) {
        if (word != null) {
            char[] chars = word.toCharArray();
            TrieNode tmp = root;
            for (int i = 0; i < chars.length; i++) {
                if(tmp.letters[chars[i]-'a'] == null)
                    tmp.letters[chars[i]-'a'] = new TrieNode();
                tmp = tmp.letters[chars[i]-'a'];
            }
            tmp.isWord = true;
        }
    }

    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        if (word != null) {
            char[] chars = word.toCharArray();
            TrieNode tmp = root;
            for (int i = 0; i < chars.length; i++) {
                if (tmp.letters[chars[i]-'a'] == null)
                    return false;
                tmp = tmp.letters[chars[i]-'a'];
            }
            return tmp.isWord;
        }
        return false;
    }

    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        char[] chars = prefix.toCharArray();
        TrieNode tmp = root;
        for (int i = 0; i < chars.length; i++) {
            if (tmp.letters[chars[i]-'a'] == null)
                return false;
            tmp = tmp.letters[chars[i]-'a'];
        }
        return true;
    }
}