LeetCode_二叉树_简单_101. 对称二叉树
2023-09-27 14:25:46 时间
1.题目
给你一个二叉树的根节点 root , 检查它是否轴对称。
示例 1:
输入:root = [1,2,2,3,4,4,3]
输出:true
示例 2:
输入:root = [1,2,2,null,3,null,3]
输出:false
提示:
树中节点数目在范围 [1, 1000] 内
-100 <= Node.val <= 100
进阶:你可以运用递归和迭代两种方法解决这个问题吗?
来源:力扣(LeetCode)
链接:https://leetcode.cn/problems/symmetric-tree
2.思路
(1)递归
3.代码实现(Java)
//思路1————递归
/**
* 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 boolean isSymmetric(TreeNode root) {
if (root == null) {
return true;
} else {
//根节点不为 null,检查其左右子树是否对称
return checkSymmetric(root.left, root.right);
}
}
public boolean checkSymmetric(TreeNode left, TreeNode right) {
if (left == null || right == null) {
return left == right;
}
if (left.val != right.val) {
return false;
}
return checkSymmetric(left.left, right.right) && checkSymmetric(left.right, right.left);
}
}
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