Symmetric Tree

Problem Summary

• Given a tree, return whether it is symmetric

What is Being Asked?

• Is left child == right child

Main Concepts Used

• Depth First Search

Time & Space Complexity

• Time: $O(n)$ → Reason: We have to visit each node
• Space: $O(h)$ → Reason: Height of tree

Code

class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        def dfs(left, right) -> bool:
            if not left and not right:
                return True
            if not left or not right:
                return False
            if left.val != right.val:
                return False
            return dfs(left.left, right.right) and dfs(left.right, right.left)

        return dfs(root.left, root.right)