Quick Overview

This question evaluates proficiency in data structures and algorithm design by testing binary search tree reconstruction from a preorder sequence and matrix spiral (clockwise layer) traversal.

Construct a BST and read spiral order

Company: Meta

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Onsite

The coding round reportedly included two algorithmic tasks: 1. **Rebuild a binary search tree from a preorder sequence** - You are given an array of distinct integers representing the preorder traversal of a binary search tree. - Reconstruct the original tree and return its root. - Aim for a solution that runs in linear time. 2. **Traverse a matrix in clockwise layers** - You are given an `m x n` integer matrix. - Return all elements in the order obtained by repeatedly visiting the current outer boundary clockwise and then shrinking the boundary until every cell has been visited.

Quick Answer: This question evaluates proficiency in data structures and algorithm design by testing binary search tree reconstruction from a preorder sequence and matrix spiral (clockwise layer) traversal.

Rebuild BST From Preorder

Return a nested [value,left,right] BST reconstructed from distinct preorder values.

Constraints

  • Inputs are Python literals matching the function signature.
  • Return a deterministic exact-match value.

Examples

Input: ([8,5,1,7,10,12],)

Expected Output: [8, [5, [1, None, None], [7, None, None]], [10, None, [12, None, None]]]

Explanation: Rebuild BST from preorder using bounds.

Input: ([],)

Expected Output: None

Explanation: Empty preorder returns None.

Hints

  1. Clarify edge cases before coding.
  2. Keep the return value deterministic.

Clockwise Matrix Layer Traversal

Return matrix elements in clockwise spiral layer order.

Constraints

  • Inputs are Python literals matching the function signature.
  • Return a deterministic exact-match value.

Examples

Input: ([[1,2,3],[4,5,6],[7,8,9]],)

Expected Output: [1, 2, 3, 6, 9, 8, 7, 4, 5]

Explanation: Clockwise layer traversal.

Input: ([[1,2,3,4]],)

Expected Output: [1, 2, 3, 4]

Explanation: Single row works.

Hints

  1. Clarify edge cases before coding.
  2. Keep the return value deterministic.

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