LeetCode/101_Symmetric_Tree.py at main · AnmolPatel20/LeetCode · GitHub

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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?

"""
# 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:
        def dfs(left, right):
            if not left and not right:
                return True
            if not left or not right:
                return False

            return ((left.val == right.val) and dfs(left.left , right.right) and dfs(left.right , right.left))
        return dfs(root.left , root.right)