Leetcode - Symmetric Tree

Leetcode : Symmetric Tree

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:

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

Example 1

Input : [1,2,2,null,3,null,3]

    1
   / \
  2   2
 / \ / \
    3   3

Output

false

Example 2

Input : [1,null, null]

    1
   / \

Output

true

Approach

Traverse through the nodes of tree using recursion - and find for cases below
i) Root Node is NULL
ii) Both Chil Nodes are NULL
iii) Left.Val == Right.Val
iv) Left.right == Right.left && Left.left == Right.right

Solutions (Python)

class Solution(object):
    def isSymmetric(self, root):
        if root is None: return True
        
        return self.solver(root.left, root.right)
    
    def solver(self, left, right):
        if left is None and right is None: return True
        if left is None or right is None: return False
        
        return left.val == right.val and self.solver(left.left, right.right) and self.solver(left.right, right.left)
        

Result

Runtime: 20 ms
Memory Usage: 12.9 MB
Runtime Beats 87.48% of Python Submission