Sig·Software Engineer·Technical Phone Screen·Junior

Junior

May 2026

Summary

SIG quant researcher interview with a logic puzzle question, the kind where you either see the path quickly or you're just staring at a grid for five minutes hoping something clicks. Pretty classic for this type of role.

Questions Asked (1)

You have a 4x4 grid where each cell must contain a building of 1 to 4 floors, with no repeated heights in any row or column. Clues on each side of the grid tell you how many buildings are visible from that direction (a taller building blocks shorter ones behind it). Given a specific set of clues, what are the heights at cells A and B?

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

This is basically a constraint satisfaction puzzle dressed up in a building metaphor.

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AI HintsAI Generated

Suggested Approach

Treat the puzzle as a constraint satisfaction problem: model the grid as a 4x4 Latin square with visibility clues, then solve systematically using deduction or backtracking. For the specific cells A and B, apply the clues to narrow possibilities, using row/column uniqueness and visibility counts to determine exact heights.

Pro tip: Demonstrate algorithmic thinking by discussing how you would code a solver (e.g., backtracking with constraint propagation) and mention that this puzzle is a classic 'Skyscrapers' problem, showing familiarity with common CS puzzles.

1. Understand the rules and constraints

Restate the problem: each row and column is a permutation of 1-4, and visibility clues indicate how many buildings are visible from each side. Clarify that taller buildings block shorter ones behind them.

2. Set up the grid and identify given clues

Draw the 4x4 grid, label cells A and B, and note the visibility numbers on each side. Identify any immediate deductions from extreme clues (e.g., a clue of 4 means the row/column must be in increasing order from that side).

3. Apply logical deduction and constraint propagation

Use the clues to eliminate possibilities: for each row/column, determine possible permutations that satisfy the visibility count and the no-repeat rule. Cross-reference rows and columns to narrow down cell values.

4. Solve for cells A and B

Once enough constraints are applied, deduce the exact heights at A and B. If stuck, consider backtracking or writing a small solver in your head, but aim for a logical solution.

5. Verify and explain

Check that the final grid satisfies all row/column uniqueness and visibility clues. Clearly state the heights at A and B and briefly explain the reasoning.

Key Points to Mention

Modeling as a constraint satisfaction problem (CSP) with variables and constraints.
The puzzle is equivalent to a 4x4 Latin square with visibility constraints.
Use of deduction techniques: extreme clues, elimination, and constraint propagation.
Algorithmic approach: backtracking search with pruning, or exact cover.
Complexity considerations: for 4x4, brute force is feasible, but for larger grids, smarter algorithms are needed.
Communication: walk through the reasoning step-by-step, even if you don't immediately know the answer.

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