.如何不用递归实现二叉树的前序/后序/中序遍历？

import java.lang.Thread.State;import java.util.ArrayDeque;import java.util.ArrayList;import java.util.List;import java.util.Queue;import java.util.Stack;public class BinaryTree {private Node root;private Node list;private Node current;public void print(){if(this.root!=null){this.root.print();}}/**       非递归中序遍历 *    思想是：用一个栈，先保存跟节点，然后循环保存的它的左子树， *    接着做出栈操作，pop出的内容的先判断他是否有右子树，如果有右子树 *    做如栈操作，然后接着判断如栈的元素是否有左子树，如果有的话，循环加入栈中 *     *              5           *             / \                          *            3   7                     *           /\   /\                     *          2  4  6                      *         /                            *         1       *     *   stack *   *  例子  左子树入栈 然后出站  *        |1|           【1】pop *        |2|           【2】pop *        |3|           【3】pop 注意呀，这个时候就得判断【3】的右子树了 *        |5|            因为3有右子树，所以的把它的右子树入栈 栈的结构图如下 *                        stack *                        【4】 *                        【5】  *                        接着同理了   */public void midPint(){Stack<Node> stack=new Stack<>();Node temp=root;if(temp!=null){stack.push(temp);}while(temp.left!=null){stack.push(temp.left);temp=temp.left;}while(stack.size()>0){temp=stack.pop();System.out.println(temp.data);if(temp.right!=null){temp=temp.right;stack.push(temp);while(temp!=null){if(temp.left!=null){stack.push(temp.left);}temp=temp.left;}}}}public List<Node> breadFirst(){List<Node> list=new ArrayList<Node>();Queue<Node> queue=new ArrayDeque<Node>();if(root!=null){queue.add(root);}while(!queue.isEmpty()){list.add(queue.peek());Node node=queue.poll();if(node.left!=null){queue.offer(node.left);}if(node.right!=null){queue.offer(node.right);}}return list;}public List<Node> breadFirst2(){List<Node> list=new ArrayList<>();Queue<Node> queue=new ArrayDeque<>();if(root!=null){queue.offer(root);}while(!queue.isEmpty()){list.add(queue.peek());Node curren=queue.poll();if(curren.left!=null){queue.offer(curren.left);}if(curren.right!=null){queue.offer(curren.right);}}return list;}/**             5           镜像后          5 *             / \                        / \  *            3   7                      7  3 *           /\   /\                    /\  /  *          2  4  6                    4  2 6  *         /                          / \  *         1                             1       * @param root */public static void preOrder(Node root){if(root==null){return;}Node temp=root.left;root.left=root.right;root.right=temp;preOrder(root.left);preOrder(root.right);}public List<Node> midPrint(Node node){List<Node> list=new ArrayList<Node>();if(node.left!=null){list.addAll(midPrint(node.left));}list.add(node);if(node.right!=null){list.addAll(midPrint(node.right));}return list;}public void converList(){if(this.root!=null){this.root.convertList();}}public void addList(Node  node){if(list==null){System.out.println("cao"+node.data);   list=node;   current=node;}else{current.right=node;node.left=current;current=node;}}public void add(int data){if(root==null){root=new Node(data, null, null);}else{Node parent = null;Node current=root;    while(current!=null){    parent=current;    if(current.data>data){    current=current.left;    }else{    current=current.right;    }        }            if(parent.data>data){    Node node=new Node(data, null, null);    parent.left=node;    }else{    Node node=new Node(data, null, null);    parent.right=node;    }}}class Node{int data;Node left;Node right;public Node(int data,Node left,Node right){this.data=data;this.left=left;this.right=right;}/** * 二差数转化成有序的链表 */public void convertList(){if(this.left!=null){this.left.convertList();}addList(this);//System.out.println(this.data);if(this.right!=null){this.right.convertList();}}public void print(){if(this.left!=null){this.left.print();}System.out.println(this.data);if(this.right!=null){this.right.print();}}@Overridepublic String toString() {// TODO Auto-generated method stubreturn ""+this.data;}}/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubBinaryTree bt = new BinaryTree();          bt.add(5);          bt.add(7);          bt.add(3);          bt.add(2);          bt.add(1);          bt.add(6);          bt.add(4);          System.out.println("************************");         bt.midPint();//        bt.preOrder(bt.root);          System.out.println("************************");        //        System.out.println(bt.breadFipreOrderrst());        bt.converList();        System.out.println("head"+bt.list.data);        Node current1=bt.list;                while(current1!=null){        System.out.println(current1.data);        current1=current1.right;        }               /* List<Node> list=bt.breadFirst2();        for(Node node:list){        System.out.println(node.data);        }*/}}