java 二叉树的镜像

题目

操作给定的二叉树，将其变换为源二叉树的镜像。

二叉树的镜像定义：         源二叉树         8       /  \      6   10     / \  / \    5  7 9 11        镜像二叉树        8       /  \      10   6     / \  / \    11 9 7  5

思路

先序遍历二叉树，判断结点是否含有左子树或右子树，有的话就交换左右子树。直到交换完所有的非叶子结点。

代码

import java.util.Stack;import java.util.LinkedList;class TreeNode {int val = 0;TreeNode left = null;TreeNode right = null;public TreeNode(int val) {this.val = val;}}public class Main {//递归public static void Mirror(TreeNode root) {if (root == null)return;if (root.left == null && root.right == null)return;TreeNode temp = root.left;root.left = root.right;root.right = temp;if(root.left!=null) Mirror(root.left);if(root.right!=null) Mirror(root.right);}//非递归public static void MirrorN(TreeNode root){if(root==null) return;Stack<TreeNode> stack=new Stack<TreeNode>();stack.push(root);while(!stack.isEmpty()){TreeNode node = stack.pop();if(node.left!=null||node.right!=null){TreeNode temp = node.left;node.left = node.right;node.right = temp;}if(node.left!=null){stack.push(node.left);}if(node.right!=null){stack.push(node.right);}}}   //层序遍历二叉树public static void levelTraverse(TreeNode root){        LinkedList<TreeNode> list= new LinkedList<TreeNode>();        list.add(root);        while(list.size() != 0){            TreeNode node = list.removeFirst();            System.out.print(node.val + " ");            if(node.left != null){                list.add(node.left);            }            if(node.right != null){                list.add(node.right);            }        }    }public static void main(String[] args) {// TODO Auto-generated method stubTreeNode root = new TreeNode(8);TreeNode a=new TreeNode(6);TreeNode b=new TreeNode(10);TreeNode aa=new TreeNode(5);TreeNode ab=new TreeNode(7);TreeNode ba=new TreeNode(9);TreeNode bb=new TreeNode(11);root.left=a;root.right=b;a.left=aa;a.right=ab;b.left=ba;b.right=bb;levelTraverse(root);MirrorN(root);System.out.println();levelTraverse(root);}}

相关知识

linkedlist详解