EasyTreesAI interview only

Symmetric Tree

Asked atamazonmicrosoftbloomberglinkedinmetagoogle

01 · Problem

Given the root of a binary tree, determine whether it is symmetric, meaning the left half is an exact mirror reflection of the right half across a vertical line through the root (both in shape and in values).

Return true if it is symmetric and false otherwise. The tree is given in level-order, with null marking a missing child. A single node is symmetric, and an empty tree is considered symmetric.

02 · Examples

Example 01

      1
    /   \
   2     2
  / \   / \
 3   4 4   3

Input

root = [1,2,2,3,4,4,3]

Output

true

The left subtree [2,3,4] mirrors the right subtree [2,4,3].

Example 02

Input

root = [1,2,2,null,3,null,3]

Output

false

Both 3s are right children; a mirror would need one of them to be a left child.

Example 03

Input

root = [1]

Output

true

A lone root is trivially its own mirror.

03 · Constraints

01The number of nodes in the tree is in the range [0, 100].
02-100 <= Node.val <= 100
03Node values may repeat, so symmetry must be checked by position, not by value alone.
04The tree height is at most 100, and the tree may be fully skewed.

04 · Optimal complexity

Time: O(n)
Space: O(h)

05 · Two ways to work on it

Practice it alone or rehearse it as an interview.

Practice Mode gives you an editor and test runs, nothing else. AI Interview Mode puts a voice interviewer on the other side, adds a clock, and ends with a scored summary of the round.

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