//postorder recursion
    public static void PostOrder(Node r)
    {
        if( r != null)
        {
            PostOrder(r.left);
            PostOrder(r.right);
            System.out.println("[" + r.data + "]");
        }
    }

    //postorder with iteration 
    //postorder with loop
	public static void PostorderIteration(Node r)
	{
		Stack<Node> st = new Stack<Node>();
        Node tmp = r;
		Node cur = r;
		
		while(!st.empty() || cur != null) 
		{
			if( cur != null)
			{ 
                st.push(cur);
				cur = cur.left;
			}
			else
			{
				Node pop = st.pop();
				if(pop.left == null && pop.right == null)
					System.out.println("p="+pop.data);
				else if(pop.right != null && pop.visited == false)
				{
					cur = pop.right;
					pop.visited = true;
					st.push(pop);
				}
				else if(pop.right != null && pop.visited == true)
					System.out.println("p="+pop.data);
			}
		}
	}

    //Postorder with two stacks
    public static void PostorderTwoStacks(Node curr)
    {
        Stack<Node> st1 = new Stack<Node>();
        Stack<Node> st2 = new Stack<Node>();
        if(curr != null)
        {
            st1.push(curr);
            while(!st1.empty())
            {
                Node node = st1.pop();
                st2.push(node);
                if(node.left != null)
                    st1.push(node.left);
                if(node.right != null)
                    st1.push(node.right);
            }
            while(!st2.empty())
            {
                Node node = st2.pop();
                System.out.println("Two Stacks Iteration["+node.data+"]");    
            }
        }
    }

class Contact implements Comparable<Contact> 
{
    String name;
    String addr;
    int    age;
    public Contact(String name, String addr, int age)
    {
        this.name = name;
        this.addr = addr;
        this.age = age;
    }

    //Minimum heap
    public int compareTo(Contact c)
    {
        return this.age - c.age;

        //Maximum heap
        //return -(this.age - c.age);
    }

    public String toString()
    {
        return "["+name+"]["+addr+"]["+age+"]";
    }
}