208. 实现 Trie (前缀树)

题解

执行用时：42 ms, 在所有 Java 提交中击败了60.29%的用户内存消耗：47.1 MB, 在所有 Java 提交中击败了91.73%的用户

class Trie {
    private Node root;
    private static class Node {
        // 当前字符
        char c;
        // 当前字符是否可构成一个单词
        boolean isWord;
        // 树的分支
        Node[] childedList;
        public Node(char c) {
            this.c = c;
            this.isWord = false;
            this.childedList = new Node[26];
        }
    }
    /** Initialize your data structure here. */
    public Trie() {
        // 树根初使化为一个空字符
        this.root = new Node(' ');
    }
    /** Inserts a word into the trie. */
    public void insert(String word) {
        int length = word.length();
        Node cur = root;
        for (int i = 0; i < length; i++) {
            char curChar = word.charAt(i);
            if (cur.childedList[curChar - 'a'] == null) {
                cur.childedList[curChar - 'a'] = new Node(curChar);
            }
            cur = cur.childedList[curChar - 'a'];
        }
        cur.isWord = true;
    }
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        Node node = searchReturnNode(word);
        if (node == null) {
            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) {
        Node node = searchReturnNode(prefix);
        return node != null;
    }
    // 返回一个节点，可以给 search 和 startsWith 方法复用
    private Node searchReturnNode(String word) {
        Node cur = root;
        for (int i = 0; i < word.length(); i++) {
            char curChar = word.charAt(i);
            if (cur.childedList[curChar - 'a'] != null) {
                cur = cur.childedList[curChar - 'a'];
            } else {
                return null;
            }
        }
        return cur;
    }
}