Symmetric Tree
Difficulty: Easy
Category: DSA
Topics: Tree, Depth-First Search, Breadth-First Search, Binary Tree
Asked at: Capital One, Amazon, Yandex, Apple, Uber, Google, Microsoft
Given the `root` of a binary tree, _check whether it is a mirror of itself_ (i.e., symmetric around its center).
**Example 1:**
**Input:** root = [1,2,2,3,4,4,3]
**Output:** true
```
**Example 2:**
**Input:** root = [1,2,2,null,3,null,3]
**Output:** false
```
**Constraints:**
- The number of nodes in the tree is in the range `[1, 1000]`.
- `-100 <= Node.val <= 100`
**Follow up:** Could you solve it both recursively and iteratively?