// 定义前缀树的节点，每个节点有一个子数组和标志位，标志位代表该节点是否为最终节点
// insert方法插入字符串，若当前节点的子数组中的对应索引位置为空，则新建前缀树的节点
// search 和 startWiths的区别在于search需要判断返回节点的isEnd属性
class TrieNode {
    TrieNode[] children;
    boolean isEnd;
    TrieNode() {
        children = new TrieNode[26];
        isEnd = false;
    } 
}
class Trie {
    TrieNode root;
    public Trie() {
        root = new TrieNode();
    }
    
    public void insert(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.isEnd = true;
    
    }
    
    public boolean search(String word) {
        TrieNode node = searchPrefix(word);
        return node != null && node.isEnd;
    }
    
    public boolean startsWith(String prefix) {
        TrieNode node = searchPrefix(prefix);
        return node != null;
    }
    public TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for (int i = 0; i < word.length(); i++) {
            int index = word.charAt(i) - 'a';
            if (node.children[index] == null) {
                return null;
            }
            node = node.children[index];
        }
        return node;
    }
    
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */