Nash AI·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Technical phone screen at Nash AI for a software engineering role. The main problem was implementing Minesweeper's click logic, which sounds like a toy problem until you're actually in it and they start asking about traversal strategy and complexity.

Questions Asked (1)

Implement the click(row, col) operation for Minesweeper, covering mine hits, zero-adjacent-mine flood fill, and numbered cell reveals. Also write a function to print the board state.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

I started with the data structures before touching any logic, which turned out to be the right call since they asked about that explicitly anyway.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the board representation and game rules, then design the click function to handle three cases: mine hit (game over), zero-adjacent-mine (flood fill using BFS/DFS), and numbered cell (simple reveal). Implement flood fill iteratively to avoid recursion depth issues, and write a print function that formats the board with hidden cells, revealed numbers, and mines appropriately.

Pro tip: Mention that you'd use an iterative BFS with a queue for flood fill to prevent stack overflow on large boards, and that you'd track visited cells to avoid infinite loops. Also, discuss how you'd extend the design to support flags and win conditions, showing foresight.

1. Clarify requirements and board representation

Ask about board size, mine placement, and cell states (hidden, revealed, flagged). Decide on a 2D array or list of lists, with separate structures for mines and revealed status.

2. Design the click operation

Outline the logic: if the cell is a mine, game over; if it has adjacent mines > 0, reveal it; if zero, reveal it and recursively reveal all adjacent cells. Use BFS/DFS for flood fill.

3. Implement flood fill iteratively

Use a queue (BFS) or stack (DFS) to process cells with zero adjacent mines, revealing neighbors and adding zero-adjacent neighbors to the queue. Mark cells as revealed to avoid reprocessing.

4. Write the board printing function

Format the board for display: hidden cells as '-', revealed empty cells as ' ', revealed numbers as digits, and mines as '*'. Consider showing all mines if game over.

5. Test with edge cases

Test clicking a mine, clicking a numbered cell, clicking a zero cell that triggers a large flood fill, and clicking an already revealed cell. Verify board printing for different states.

Key Points to Mention

Handling mine hit: immediately end game and reveal all mines.
Flood fill algorithm: BFS vs DFS, iterative vs recursive, and avoiding stack overflow.
Tracking visited/revealed cells to prevent infinite loops and redundant work.
Calculating adjacent mine counts efficiently (e.g., precompute or compute on the fly).
Board printing: clear formatting, handling hidden vs revealed cells, and game-over state.
Time and space complexity: O(R*C) for flood fill in worst case, O(1) for numbered reveal.

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