Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Meta SWE coding round, one geometry problem that looked deceptively simple. The kind of question where you feel good for the first five minutes and then realize you've been thinking about it wrong the whole time.

Questions Asked (1)

Given a set of 2D points with integer coordinates, find all groups of four points that form a rectangle. Output each valid combination sorted by x and y coordinates, one per line.

Algorithms & Data Structures

Author's notes

My first instinct was brute force all combinations of four points and check each one, which works but is slow and I knew they'd push back on it.

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AI HintsAI Generated

Suggested Approach

Clarify the problem constraints (input size, coordinate ranges, output format) and propose an efficient algorithm. A common approach is to group points by x-coordinate, then for each pair of x-coordinates, find matching y-coordinates that form rectangles. Alternatively, use a hash set of points and iterate over pairs of points as potential diagonals, checking if the other two corners exist.

Pro tip: Mention that rectangles can be identified by their diagonals: for any two points that can serve as opposite corners, the other two corners are determined. This reduces the problem to checking pairs of points and using a hash set for O(1) lookups, yielding O(n^2) time complexity.

1. Clarify requirements and constraints

Ask about input size, coordinate ranges, whether points are unique, and the exact output format (e.g., sorted by x and y, one per line). Confirm if rectangles can be axis-aligned only or any orientation.

2. Choose an efficient algorithm

Decide between approaches: (a) group by x and y coordinates, (b) use diagonal property with hash set. Explain the time and space complexity of each and justify your choice.

3. Outline the algorithm steps

Describe how to iterate over pairs of points, compute the other two corners, and check for their existence. Emphasize avoiding duplicate rectangles by enforcing an ordering (e.g., only consider pairs where x1 < x2 and y1 < y2).

4. Handle output and sorting

Explain how to collect valid rectangles, sort them by x and y coordinates (e.g., sort the four points within each rectangle, then sort the list of rectangles), and output one per line.

5. Analyze complexity and edge cases

State time and space complexity (e.g., O(n^2) time, O(n) space). Discuss edge cases: no rectangles, duplicate points, collinear points, and large inputs.

Key Points to Mention

Use a hash set for O(1) point lookups to check existence of computed corners.
Leverage the diagonal property: two points define a rectangle if the other two corners exist.
Avoid duplicates by enforcing a consistent ordering of points (e.g., only consider pairs where x1 < x2 and y1 < y2).
Time complexity: O(n^2) with hash set, which is optimal for this problem.
Space complexity: O(n) for storing points in a set.
Output format: sort each rectangle's points by x then y, and sort all rectangles lexicographically.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.