208. Implement Trie (Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Note: You may assume that all inputs are consist of lowercase letters a-z.

insert: time O(m) space O(m)

search: time O(m) space O(1)

class TrieNode {
    private TrieNode[] links;
    private final int R = 26;
    private boolean isEnd;
    
    // Initialize your data structure here.
    public TrieNode() {
        links = new TrieNode[R];
    }
    
    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 void setEnd() {
        isEnd = true;
    }
    
    public boolean isEnd() {
        return isEnd;
    }
}

public class Trie {
    private TrieNode root;

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

    // Inserts a word into the trie.
    public void insert(String word) {
        TrieNode node = root;
        for(char ch : word.toCharArray()) {
            if(!node.containsKey(ch)) {
                node.put(ch, new TrieNode());
            }
            node = node.get(ch);
        }
        node.setEnd();
    }
    
    public TrieNode searchPrefix(String word) {
        TrieNode node = root;
        for(char ch : word.toCharArray()) {
            if(!node.containsKey(ch)) return null;
            node = node.get(ch);
        }
        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;
    }
}

// Your Trie object will be instantiated and called as such:
// Trie trie = new Trie();
// trie.insert("somestring");
// trie.search("key");