import java.util.*;

public class TreeTraversal {

        static class Node<T> {
		T value;
		Node<T> left;
		Node<T> right;

		Node(T value) {
			this.value = value;
		}

		void visit() {
			System.out.print(this.value + " ");
		}
	}

	static enum ORDER {
		PREORDER, INORDER, POSTORDER, LEVEL
	}

        static <T> void traverse(Node<T> node, ORDER order) {
		if (node == null) {
			return;
		}
		switch (order) {
		case PREORDER:
			node.visit();
			traverse(node.left, order);
			traverse(node.right, order);
			break;
		case INORDER:
			traverse(node.left, order);
			node.visit();
			traverse(node.right, order);
			break;
		case POSTORDER:
			traverse(node.left, order);
			traverse(node.right, order);
			node.visit();
			break;
		case LEVEL:
			Queue<Node<T>> queue = new LinkedList<>();
			queue.add(node);
			while(!queue.isEmpty()){
				Node<T> next = queue.remove();
				next.visit();
				if(next.left!=null)
					queue.add(next.left);
				if(next.right!=null)
					queue.add(next.right);
			}
		}
	}	

	public static void main(String[] args) {

		Node<Integer> one = new Node<Integer>(1);
		Node<Integer> two = new Node<Integer>(2);
		Node<Integer> three = new Node<Integer>(3);
		Node<Integer> four = new Node<Integer>(4);
		Node<Integer> five = new Node<Integer>(5);
		Node<Integer> six = new Node<Integer>(6);
		Node<Integer> seven = new Node<Integer>(7);
		Node<Integer> eight = new Node<Integer>(8);
		Node<Integer> nine = new Node<Integer>(9);
		
		one.left = two;
		one.right = three;
		two.left = four;
		two.right = five;
		three.left = six;
		four.left = seven;
		six.left = eight;
		six.right = nine;

		traverse(one, ORDER.PREORDER);
		System.out.println();
		traverse(one, ORDER.INORDER);
		System.out.println();
		traverse(one, ORDER.POSTORDER);
		System.out.println();
		traverse(one, ORDER.LEVEL);
		
	}
}
