Trie Autocomplete

Trie.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;


public class TrieNode {
	char c;
	Map<Character, TrieNode> children;
	boolean isWord;

	public TrieNode(char c) {
		this.c = c;
		children = new HashMap<>();
	}

	public TrieNode() {
		children = new HashMap<>();
	}

	public void insert(String word) {
		if (word == null || word.isEmpty())
			return;
		char firstChar = word.charAt(0);
		TrieNode child = children.get(firstChar);
		if (child == null) {
			child = new TrieNode(firstChar);
			children.put(firstChar, child);
		}

		if (word.length() > 1)
			child.insert(word.substring(1));
		else
			child.isWord = true;
	}

}




public class Trie {
	TrieNode root;

	public Trie(List<String> words) {
		root = new TrieNode();
		for (String word : words)
			root.insert(word);

	}

	public boolean find(String prefix /*,boolean exact*/) {
		TrieNode lastNode = root;
		for (char c : prefix.toCharArray()) {
			lastNode = lastNode.children.get(c);
			if (lastNode == null)
				return false;
		}
		return lastNode.isWord;
		// return !exact || lastNode.isWord;
	}

	/*public boolean find(String prefix) {
		return find(prefix, false);
	}*/

	public void suggestHelper(TrieNode root, List<String> list, StringBuffer curr) {
		if (root.isWord) {
			list.add(curr.toString());
		}

		if (root.children == null || root.children.isEmpty())
			return;

		for (TrieNode child : root.children.values()) {
			suggestHelper(child, list, curr.append(child.c));
			curr.setLength(curr.length() - 1);
		}
	}

	public List<String> suggest(String prefix) {
		List<String> list = new ArrayList<>();
		StringBuffer curr = new StringBuffer();
		
		TrieNode lastNode = root;
		
		for (char c : prefix.toCharArray()) {
			lastNode = lastNode.children.get(c);
			if (lastNode == null)
				return list;
			curr.append(c);
		}
		suggestHelper(lastNode, list, curr);
		return list;
	}


	public static void main(String[] args) {
		List<String> words = List.of("hello", "dog", "hell", "cat", "a", "hel","help","helps","helping");
		Trie trie = new Trie(words);
	
		System.out.println(trie.suggest("hel"));
	}

}