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Symmetric Tree

Problem Statement​

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

Leetcode Link

Example 1:​

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

Example 2:​

alt text

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

Code​

Python
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        left_stack = [root.left]
        right_stack = [root.right]

        right_visited = []
        left_visited = []

        while len(left_stack) != 0:
            curr = left_stack.pop()
            if curr:
                left_visited.append(curr.val)
                left_stack.append(curr.right)
                left_stack.append(curr.left)
            else:
                left_visited.append(None)

        while len(right_stack) != 0:
            curr = right_stack.pop()
            if curr:
                right_visited.append(curr.val)
                right_stack.append(curr.left)
                right_stack.append(curr.right)
            else:
                right_visited.append(None)

        return left_visited == right_visited