sunrise·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Jun 2026

Summary

Interviewed for a software engineering role at Sunrise and got hit with a math-heavy matrix problem that I wasn't really expecting. The whole session was pretty focused on deriving values without brute force, which was a good challenge but also a bit stressful when you're on the spot.

Questions Asked (1)

Given an n×n matrix filled in spiral order, compute the value at a given coordinate (x, y) without actually building the matrix. The solution should run in constant time and constant space.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I spent the first few minutes trying to mentally simulate the spiral which was a mistake.

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AI HintsAI Generated

Suggested Approach

First, determine which concentric layer the coordinate (x, y) belongs to by computing the minimum distance to any edge. Then, calculate the starting value of that layer and the offset along the spiral path to the coordinate, using the layer's dimensions and the coordinate's position on the top, right, bottom, or left side.

Pro tip: Clarify whether the spiral starts at (0,0) and proceeds clockwise, and confirm the coordinate system (0-indexed vs 1-indexed). Also, mention that the solution can be adapted to any spiral order by adjusting the offset calculation.

1. Clarify assumptions

Confirm the spiral direction (clockwise/counterclockwise), starting point, and indexing convention. This ensures the formula matches the expected output.

2. Identify the layer

Compute the layer index L = min(x, y, n-1-x, n-1-y). This determines which concentric square the coordinate lies on.

3. Compute starting value of layer

Calculate the total number of elements in all outer layers: start = n^2 - (n - 2L)^2. This is the value at the top-left corner of layer L.

4. Calculate offset within layer

Determine the position along the spiral path: if on top edge, offset = y - L; if on right edge, offset = (side-1) + (x - L); if on bottom edge, offset = 2*(side-1) + (n-1-L - y); if on left edge, offset = 3*(side-1) + (n-1-L - x), where side = n - 2L.

5. Return final value

The value at (x, y) is start + offset. Verify with a small example (e.g., n=3) to ensure correctness.

Key Points to Mention

Time and space complexity: O(1) time and O(1) space, as no matrix is built.
Layer-based decomposition: the spiral can be viewed as concentric square layers.
Offset calculation: mapping the coordinate to a linear index along the spiral path.
Edge cases: coordinates on corners, center element (when n is odd), and n=1.
Generalization: the approach can be adapted to different spiral directions or starting points.
Verification: testing with small matrices to validate the formula.

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