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226 翻转二叉树

秀儿2020 2022-02-19 阅读 73

题目

给你一棵二叉树的根节点 root ,翻转这棵二叉树,并返回其根节点
交换节点的左右子节点即可实现题目所说的翻转
示例:
在这里插入图片描述

代码

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null){
            return root;
        }

        Queue<TreeNode> queue = new LinkedList<TreeNode>();
        queue.offer(root);

        while(!queue.isEmpty()){
            int currentLevelSize = queue.size(); 

            for(int i = 0; i < currentLevelSize; i++){
                //用来从队列头部删除一个元素。
                TreeNode node = queue.poll();

                TreeNode temp = node.left;
                node.left = node.right;
                node.right = temp;
               
                if(node.left != null){
                    queue.offer(node.left);
                }
                if(node.right != null){
                    queue.offer(node.right);
                }
            }
        }
        return root;
    }
}
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