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

• Difficulty: EASY

Input: [1,2,2,3,4,4,3]
    1
   / \
  2   2
 / \ / \
3  4 4  3

Output: true

Input: [1,2,2,null,3,null,3]
    1
   / \
  2   2
   \   \
   3    3
Output: false

• Bonus points if you could solve it both recursively and iteratively.

1. Iteration - BFS
   • Time complexity: $O(n)$
   • Space complexity: $O(n)$
2. Recursion
   • Time complexity: $O(n)$
   • Space complexity: $O(n)$