Check Reflected Binary-Tree Structure and Values
Company: Amazon
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
Determine whether a binary tree is symmetric about its root: its left and right sides must be mirror images with equal values in corresponding reflected positions. Both shape and values matter.
Use the supplied `TreeNode` fields `val`, `left`, and `right`:
```cpp
bool isSymmetric(TreeNode* root);
```
Level-order examples use `null` for missing children; the actual argument is a node pointer.
### Examples
```text
Input: root = [5,2,2,1,4,4,1]
Output: true
```
```text
Input: root = [6,3,3,null,2,null,2]
Output: false
```
The two nodes valued 2 both occupy right-child positions, rather than reflected positions.
### Constraints
- The tree contains between 1 and 1000 nodes.
- Node values lie between -100 and 100, inclusive.
### Source follow-up
Consider both recursive and iterative solutions.
Overview: Check binary-tree mirror symmetry in both structure and values, with recursive and iterative approaches.
