Java implementation LeetCode 208 to achieve Trie (Prefix Tree)

208. realize Trie (Prefix Tree)

Implement a Trie (prefix tree), comprising insert, search, and startsWith these three operations.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // 返回 true
trie.search("app");     // 返回 false
trie.startsWith("app"); // 返回 true
trie.insert("app");   
trie.search("app");     // 返回 true

Description:

You can assume that all inputs are constituted by the lowercase letters az.
To ensure that all inputs are non-empty string.

class Trie {

     class Node {
        boolean isWord;
        Node[] next = new Node[26];
    }
    
    Node root = new Node();
    
    /** Initialize your data structure here. */
    public Trie() {
        
    }
    
    /** Inserts a word into the trie. */
    public void insert(String word) {
        Node p = root;
        for(char ch : word.toCharArray()) {
            if(p.next[ch - 'a'] == null)
                p.next[ch - 'a'] = new Node();
            p = p.next[ch - 'a'];
        }
        p.isWord = true;
    }
    
    /** Returns if the word is in the trie. */
    public boolean search(String word) {
        Node p = root;
        for(char ch : word.toCharArray()) {
            if(p.next[ch - 'a'] == null)
                return false;
            p = p.next[ch - 'a'];
        }
        return p.isWord;
    }
    
    /** Returns if there is any word in the trie that starts with the given prefix. */
    public boolean startsWith(String prefix) {
        Node p = root;
        for(char ch : prefix.toCharArray()) {
            if(p.next[ch - 'a'] == null)
                return false;
            p = p.next[ch - 'a'];
        }
        return true;
    }
}

/**
 * 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);
 */