class Node{
	public int val;
	public Node left;
	public Node right;
	
	public Node(int v) {
		val=v;
		left=null;
		right=null;
	}
}

public class Main {
	public static void main(String[] args) {
		Node head =new Node(0);
		Node node1=new Node(1);
		Node node2=new Node(2);
		Node node3=new Node(3);
		Node node4=new Node(4);
		Node node5=new Node(5);
		Node node6=new Node(6);
		head.left=node1;
		head.right=node2;
		node1.left=node3;
		node1.right=node4;
		node2.left=node5;
		node2.right=node6;
		pos2(head);
		pos1(head);
		in(head);
	}

public static void pos1(Node h) {
	System.out.print("先序遍歷 ");
	if(h!=null) {
		Stack<Node>stack =new Stack<Node>();
		stack.push(h);
		while(!stack.isEmpty()) {
			h=stack.pop();
			System.out.print(h.val+" ");
			if(h.right!=null) {
				stack.push(h.right);
			}
			if(h.left!=null) {
				stack.push(h.left);
			}
		}
	}
	System.out.println();
}

public static void in(Node h) {
	System.out.print("中序遍歷 ");
	if(h!=null) {
		Stack<Node>stack =new Stack<Node>();
		while(!stack.isEmpty()||h!=null) {
			if(h!=null) {
				stack.push(h);
				h=h.left;
			}else {
				h=stack.pop();
				System.out.print(h.val+" ");
				h=h.right;
			}
		}
	}
	System.out.println();
}

public static void pos2(Node h) {
	if(h!=null) {
		Stack<Node>stack =new Stack<Node>();
		stack.push(h);
		Node c=null;//用c記錄上一次被打印的節(jié)點(diǎn)
		while(!stack.isEmpty()) {
			c=stack.peek();
			if(c.left!=null&&h!=c.left&&h!=c.right) {
				stack.push(c.left);
			}else if(c.right!=null&&h!=c.right) {
				stack.push(c.right);
			}else {
				System.out.print(stack.pop().val+" ");
				h=c;//記錄本次被打印的節(jié)點(diǎn)
			}
		}
	}
}