EasyTreesAI interview only
Invert Binary Tree
Asked atgoogleamazonmetamicrosoftapplebloomberg
01 · Problem
You are handed the root of a binary tree. Flip the tree into its mirror image: at every node, the left child becomes the right child and vice versa. Return the root of the flipped tree.
The tree is given in level-order, with null marking a missing child. The expected output is the level-order serialization of the mirrored tree (trailing nulls omitted).
02 · Examples
Example 01
4 4 / \ / \ 2 7 => 7 2 / \ / \ / \ / \ 1 3 6 9 9 6 3 1
Input
root = [4,2,7,1,3,6,9]
Output
[4,7,2,9,6,3,1]
Swapping children at every level reverses each level: [2,7] becomes [7,2] and [1,3,6,9] becomes [9,6,3,1].
Example 02
Input
root = [2,1,3]
Output
[2,3,1]
The root's two children trade places.
Example 03
Input
root = []
Output
[]
An empty tree mirrors to an empty tree.
03 · Constraints
- 01The number of nodes in the tree is in the range [0, 100].
- 02-100 <= Node.val <= 100
- 03The tree height is at most 100, and the tree may be fully skewed.
- 04Node values are not necessarily unique.
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.