문제Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center). 예제 1 Input: root = [1,2,2,3,4,4,3]Output: true 예제 2 Input: root = [1,2,2,null,3,null,3]Output: false 제약조건✅ The number of nodes in the tree is in the range [1, 1000]. ✅ -100 문제풀이/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * ..