208. Implement Trie (Prefix Tree)

缺乏、安全感 2022-04-24 15:34 141阅读 0赞

Implement a trie with insert, search, and startsWith methods.
    
    Example:
    
    Trie trie = new Trie();
    
    trie.insert("apple");
    trie.search("apple");   // returns true
    trie.search("app");     // returns false
    trie.startsWith("app"); // returns true
    trie.insert("app");   
    trie.search("app");     // returns true
    Note:
    
    You may assume that all inputs are consist of lowercase letters a-z.
    All inputs are guaranteed to be non-empty strings.

本题考查的前缀树的知识点，个人觉得该题的[Solution][]写得特别好。

照例贴代码如下：

/**
     * 208. Implement Trie (Prefix Tree)
     * 前缀树的节点定义
     */
    class TrieNode {
        private TrieNode[] links;//最多有26个子节点
        private final int MAX_NODE = 26;
        private boolean isEnd;//判断该节点是否是尾结点（即是否存在从根节点到该节点的单词）
    
        public TrieNode() {
            links = new TrieNode[MAX_NODE];
        }
    
        public boolean containsKey(char ch) {
            return links[ch-'a'] != null;
        }
    
        public TrieNode get(char ch) {
            return links[ch-'a'];
        }
    
        public void put(char ch, TrieNode node) {
            links[ch-'a'] = node;
        }
    
        public boolean isEnd() {
            return isEnd;
        }
    
        public void setEnd(boolean end) {
            isEnd = end;
        }
    }
    
    class Trie {
        private TrieNode root;//前缀树的根节点
    
        /** Initialize your data structure here. */
        public Trie() {
            root = new TrieNode();
        }
    
        /** Inserts a word into the trie. */
        public void insert(String word) {
            TrieNode node = root;
            for(int i = 0; i < word.length(); ++i) {
                char ch = word.charAt(i);
                if(!node.containsKey(ch)) {
                    node.put(ch, new TrieNode());
                }
                node = node.get(ch);
            }
            node.setEnd(true);
        }
    
        private TrieNode searchPrefix(String word) {
            TrieNode node = root;
            for(int i = 0; i < word.length(); ++i) {
                char ch = word.charAt(i);
                if(node.containsKey(ch)) {
                    node = node.get(ch);
                } else {
                    return null;
                }
            }
            return node;
        }
    
        /** Returns if the word is in the trie. */
        public boolean search(String word) {
            TrieNode node = searchPrefix(word);
            return node != null && node.isEnd();
        }
    
        /** Returns if there is any word in the trie that starts with the given prefix. */
        public boolean startsWith(String prefix) {
            TrieNode node = searchPrefix(prefix);
            return node != null;
        }
    }

[Solution]: https://leetcode.com/problems/implement-trie-prefix-tree/solution/