递归和非递归的方式实现二叉树的先序、中序和后序遍历

import java.util.Stack;

/**
 * Created by lxw, [email protected] on 2017/10/30.
 * 
 */
public class PreOrder_InOrder_PosOrder {

    public class Node{
        public int value;
        public Node left;
        public Node right;

        public Node(int data){
            this.value = data;
        }
    }
    
    public void PreOrderRecur(Node head){
        if(head == null){
            return;
        }
        System.out.print(head.value + " ");
        PreOrderRecur(head.left);
        PreOrderRecur(head.right);
    }
    
    public void InOrderRecur(Node head){
        if(head == null){
            return;
        }
        InOrderRecur(head.left);
        System.out.print(head.value + " ");
        InOrderRecur(head.right);
    }
    
    public void PosOrderRecur(Node head){
        if(head == null){
            return;
        }
        PosOrderRecur(head.left);
        PosOrderRecur(head.right);
        System.out.print(head.value + " ");
    }
    
    public void PreOrderUnRecur(Node head){
        if(head == null){
            return;
        }
        Stack<Node> stack = new Stack<Node>();
        stack.push(head);
        while (!stack.isEmpty()){
            head = stack.pop();
            System.out.print(head.value + " ");
            if(head.right != null){
                stack.push(head.right);
            }
            if(head.left != null){
                stack.push(head.left);
            }
        }
        System.out.println();
    }
    
    public void InOrderUnRecur(Node head){
        if(head == null){
            return;
        }
        Stack<Node> stack = new Stack<Node>();
        while (!stack.isEmpty() || head != null){
            if(head != null){
                stack.push(head);
                head = head.left;
            } else {
                head = stack.pop();
                System.out.print(head.value + " ");
                head = head.right;
            }
        }
        System.out.println();
    }
    
    public PosOrderUnRecur(Node head){
        if(head == null){
            return;
        }
        Stack<Node> stack1 = new Stack<Node>();
        Stack<Node> stack2 = new Stack<Node>();
        stack1.push(head);
        while (!stack1.isEmpty()){
            head = stack1.pop();
            stack2.push(head);
            if(head.left != null){
                stack1.push(head.left);
            }
            if(head.right != null){
                stack1.push(head.right);
            }
        }
        while (!stack2.isEmpty()){
            System.out.print(stack2.pop().value + " ");
        }
        System.out.println();
    }
    
    
}