剑指offer系列16---二叉树的镜像

  1 package com.exe4.offer;
  2 import java.util.Stack;
  3 
  4 /**
  5  * 16【题目】二叉树的镜像
  6  *    【思路】方法一：采用递归方式进行交换，先交换根节点的左右节点，接着交换左右结点的左右结点
  7  *             方法二：采用非递归方式，即依次遍历左右子树结点依次交换,采用栈操作方式stack
  8  * @author WGS
  9  *
 10  */
 11 public class TreeMirror {
 12     //二叉树结点定义
 13     public static class TreeNode {
 14         int val = 0;
 15         TreeNode left = null;
 16         TreeNode right = null;
 17 
 18         public TreeNode(int val) {
 19             this.val = val;
 20 
 21         }
 22 
 23     }
 24     //采用递归方式进行交换，先交换根节点的左右节点，接着交换左右结点的左右结点
 25     public void mirrorExchange(TreeNode node){
 26         if(node==null || node.left==null || node.right==null){
 27             return;
 28         }
 29         //开始交换根节点的左右结点
 30         TreeNode tempNode=null;
 31         tempNode=node.left;
 32         node.left=node.right;
 33         node.right=tempNode;
 34         
 35         //继续交换
 36         if(node.left!=null)
 37             mirrorExchange(node.left);
 38         if(node.right!=null)
 39             mirrorExchange(node.right);
 40     }
 41     //采用非递归方式，即依次遍历左右子树结点依次交换,采用栈操作方式s
 42     public void mirrorExchange2(TreeNode root){
 43         if(root==null || root.left==null || root.right==null){
 44             return;
 45         }
 46          Stack<TreeNode> stack = new Stack<TreeNode>();
 47          stack.push(root);
 48          while(!stack.isEmpty()){
 49              TreeNode node=stack.pop();
 50              //交换左右结点
 51              TreeNode temp=node.left;
 52              node.left=node.right;
 53              node.right=temp;
 54              //继续遍历下一个左右结点
 55              if(node.left!=null)
 56                  stack.push(node.left);
 57              if(node.right!=null)
 58                  stack.push(node.right);
 59          }
 60     }
 61 
 62     //前序遍历1
 63     public void preInOreder(TreeNode T){
 64         if(T==null) return;
 65         System.out.println(T.val);
 66         preInOreder(T.left);
 67         preInOreder(T.right);
 68     }
 69      //前序遍历2
 70     public void preOrderTarverse(TreeNode root) {
 71         Stack<TreeNode> s = new Stack<TreeNode>();
 72         while (root != null || !s.isEmpty()) {
 73             //遍历左子树
 74             while (root != null) {
 75                 System.out.println(root.val);
 76                 s.push(root);
 77                 root = root.left;
 78             }
 79             // 左子树遍历结束，继续遍历右子树
 80             if (!s.isEmpty()) {
 81                 root = s.pop();
 82                 root = root.right;
 83             }
 84         }
 85     }
 86 
 87     public static void main(String[] args) {
 88         TreeNode root = new TreeNode(8);
 89         TreeNode node1 = new TreeNode(6);
 90         TreeNode node2 = new TreeNode(10);
 91         TreeNode node3 = new TreeNode(5);
 92         TreeNode node4 = new TreeNode(7);
 93         TreeNode node5 = new TreeNode(9);
 94         TreeNode node6 = new TreeNode(11);
 95 
 96         root.left = node1;
 97         root.right = node2;
 98         node1.left = node3;
 99         node1.right = node4;
100         node2.left = node5;
101         node2.right = node6;
102 
103         TreeMirror r = new TreeMirror();
104         r.mirrorExchange2(root);
105 
106         r.preOrderTarverse(root);
107     }
108 }