Symmetric tree

# 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 compare(self, left, right) -> bool:
        if left is None and right is not None: return False
        elif left is not None and right is None: return False
        elif left is None and right is None: return True
        elif left.val != right.val: return False

        outside = self.compare(left.left, right. right)
        inner = self.compare(left.right, right.left)
        return outside and inner

    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        if not root:
            return root
        return self.compare(root.left, root.right)

Symmetric Tree

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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

 

Follow up: Could you solve it both recursively and iteratively?