Symmetric Binary Tree

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

1 <= number of nodes <= 10⁵

First and only argument is the root node of the binary tree.

Return 0 / 1 ( 0 for false, 1 for true ).

Input 1:

    1
   / \
  2   2
 / \ / \
3  4 4  3

Input 2:

    1
   / \
  2   2
   \   \
   3    3

Output 1:

 1

Output 2:

 0

Explanation 1:

 The above binary tree is symmetric. 

Explanation 2:

The above binary tree is not symmetric.