208. Implement Trie (Prefix Tree)

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.

实现一个trie树

class Trie {


    class Node {
        Node[] next = new Node[27];
    }

    Node endNode = new Node();
    Node root = new Node();

    /** Initialize your data structure here. */
    public Trie() {
        
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        Node curNode = root;
        for (char c : word.toCharArray()) {
            if (curNode.next[c - 'a'] == null) {
                curNode.next[c - 'a'] = new Node();
            }
            curNode = curNode.next[c - 'a'];
        }
        curNode.next[26] = endNode;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        return search(word, true);
    }

    public boolean search(String word, boolean mustEnd) {
        Node curNode = root;
        for (char c : word.toCharArray()) {
            if (curNode.next[c - 'a'] == null) return false;
            curNode = curNode.next[c - 'a'];
        }
        return mustEnd ? curNode.next[26] != null : true;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        return search(prefix, false);
    }
}