208. 实现 Trie (前缀树)

public class Num208实现Trie前缀树 {
    class Trie {
        //前缀树结点
        private class TrieNode {
            //是否有以这个字符结尾的单词
            boolean isEnd;
            //儿子结点
            TrieNode[] next;

            public TrieNode() {
                isEnd = false;
                next = new TrieNode[26];
            }
        }
        //根结点
        private TrieNode root;

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

        public void insert(String word) {
            TrieNode node = root;
            for (char c : word.toCharArray()) {
                if(node.next[c-'a']==null){
                    node.next[c - 'a'] = new TrieNode();
                }
                node = node.next[c - 'a'];
            }
            node.isEnd = true;
        }


        public boolean search(String word) {
            TrieNode node = root;
            for (char c : word.toCharArray()) {
                node = node.next[c - 'a'];
                if(node==null) return false;
            }
            return node.isEnd;
        }


        public boolean startsWith(String prefix) {
            TrieNode node = root;
            for (char c : prefix.toCharArray()) {
                node = node.next[c - 'a'];
                if(node==null) return false;
            }
            return true;
        }
    }
}