// https://en.wikipedia.org/wiki/Trie
public class Trie {
	static class TrieNode {
		TrieNode[] children = new TrieNode[128];
		boolean leaf;
	}

	public static void insertString(TrieNode root, String s) {
		TrieNode cur = root;
		for (char ch : s.toCharArray()) {
			if (cur.children[ch] == null) {
				cur.children[ch] = new TrieNode();
			}
			cur = cur.children[ch];
		}
		cur.leaf = true;
	}

	public static void printSorted(TrieNode node, String s) {
		for (char ch = 0; ch < node.children.length; ch++) {
			TrieNode child = node.children[ch];
			if (child != null)
				printSorted(child, s + ch);
		}
		if (node.leaf) {
			System.out.println(s);
		}
	}

	// Usage example
	public static void main(String[] args) {
		TrieNode root = new TrieNode();
		insertString(root, "hello");
		insertString(root, "world");
		insertString(root, "hi");
		printSorted(root, "");
	}
}