1 前言 

LeetCode连接

根据二叉树的根节点root，反转这棵二叉树，并返回其根节点。

 

 2 思路

总体思想是采用层序遍历《Java 一文详解二叉树的层序遍历》

【第一步】交换root的左右子节点

 【第二步】交换节点7的左右子节点

 【第三步】交换节点2的左右子节点

package cn.msf.tree;import javax.xml.namespace.QName;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.List;import static cn.msf.tree.LevelTraversal.levelPrint;/*** @author : msf* @date : 2022/12/6*/
public class InvertTree {public static void main(String[] args) {TreeNode root = new TreeNode(1);TreeNode node1 = new TreeNode(2);TreeNode node2 = new TreeNode(3);TreeNode node3 = new TreeNode(4);TreeNode node4 = new TreeNode(5);TreeNode node5 = new TreeNode(6);TreeNode node6 = new TreeNode(7);root.left = node1;root.right = node2;node1.left = node3;node1.right = node4;node2.left = node5;node2.right = node6;System.out.println("反转前 二叉树的层序遍历结果");List<ArrayList<Integer>> arrayLists = levelPrint(root);for (ArrayList<Integer> arrayList : arrayLists) {System.out.println(arrayList);}InvertTree tree = new InvertTree();root = tree.invertTree(root);System.out.println("反转后 二叉树的层序遍历结果");arrayLists  = levelPrint(root);for (ArrayList<Integer> arrayList : arrayLists) {System.out.println(arrayList);}}public TreeNode invertTree(TreeNode root) {if (root == null) {return null;}Deque<TreeNode> queue = new ArrayDeque<>();queue.addLast(root);while (!queue.isEmpty()) {int size = queue.size();for (int i = 0; i < size; i++) {TreeNode node = queue.removeFirst();if (node.left != null) {queue.addLast(node.left);}if (node.right != null) {queue.addLast(node.right);}if(node.left != null || node.right !=null) {TreeNode temp = node.left;node.left = node.right;node.right = temp;}}}return root;}
}

上述代码执行结果：