101. 对称二叉树
难度简单1872
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?
/**
* 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;
return p(root.left,root.right);
}
private boolean p(TreeNode left, TreeNode right) {
if(left==null&&right==null)
return true;
if(left==null||right == null)
return false;
if(left.val != right.val)
return false;
return p(left.right,right.left)
&&p(left.left,right.right);
}
}
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