LeetCode - Symmetric Tree

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

 

Example 1:

Input: root = [1,2,2,3,4,4,3]
Output: true

Example 2:

Input: root = [1,2,2,null,3,null,3]
Output: false

 

Constraints:

• The number of nodes in the tree is in the range [1, 1000].
• -100 <= Node.val <= 100

 

My Solution:

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        if root.left is None and root.right is None:
            return True
        elif root.left is None or root.right is None:
            return False
        elif root.left.val != root.right.val:
            return False
        
        def invertTree(root: Optional[TreeNode]) -> Optional[TreeNode]:
            if root is None or root.left is None and root.right is None:
                return root
            
            root.left, root.right = invertTree(root.right), invertTree(root.left)
            return root
        
        def isSameTree(p: Optional[TreeNode], q: Optional[TreeNode]) -> bool:
            if p is None and q is None:
                return True
            
            if p is None or q is None:
                return False
            
            if p.val != q.val:
                return False

            if not isSameTree(p.left, q.left) or not isSameTree(p.right, q.right):
                return False
            
            return True
        
        return isSameTree(root.left, invertTree(root.right))