# Problem Definition

## Description

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree `[1,2,2,3,4,4,3]` is symmetric:

```plaintext
    1
   / \
  2   2
 / \ / \
3  4 4  3
```

But the following `[1,2,2,null,3,null,3]` is not:

```plaintext
    1
   / \
  2   2
   \   \
   3    3
```

**Note:**
Bonus points if you could solve it both recursively and iteratively.

## Notes

1. [LeetCode discussion - Recursive and non-recursive solutions in Java](https://leetcode.com/explore/interview/card/top-interview-questions-easy/94/trees/627/discuss/33054/Recursive-and-non-recursive-solutions-in-Java)