Databricks·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026Remote

Summary

Databricks coding round focused on a classic game logic problem, but the real test was whether you'd spot the optimization angle. Pretty standard for a mid-to-senior engineering screen.

Questions Asked (1)

Design and implement a Tic-Tac-Toe class with a move(row, col, player) method that returns the current game state after each move. How do you make each move check run in O(1) time?

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

I got the basic implementation working fine, class with a 2D board, checking rows and columns and diagonals after each move.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements and constraints, then propose an O(1) move validation using row, column, and diagonal counters. Implement the TicTacToe class with a move method that updates these counters and checks for a win in constant time, and discuss trade-offs and edge cases.

Pro tip: Mention that you would use separate arrays for rows, columns, and two variables for diagonals, and that you can optimize space by using a single array of size 2*n+2. Also, highlight that the O(1) check is possible because each move only affects one row, one column, and possibly two diagonals.

1. Clarify requirements and constraints

Ask about board size (fixed 3x3 or variable n x n), number of players, and whether invalid moves need handling. Confirm that the move method should return the current game state (e.g., win, draw, ongoing).

2. Design data structures for O(1) updates

Use arrays to track counts for each row and column, and variables for the two diagonals. For an n x n board, maintain an array of size 2n+2 where each index represents a row, column, or diagonal.

3. Implement the move method

On each move, update the corresponding row, column, and diagonal counters (if applicable) by adding +1 for player 1 and -1 for player 2. Check if any counter reaches +n or -n to determine a win.

4. Handle game state and edge cases

Track the number of moves to detect a draw. Validate that the move is within bounds and the cell is empty. Return the appropriate state (e.g., 'X wins', 'O wins', 'Draw', 'Next turn').

5. Analyze complexity and trade-offs

Explain that each move is O(1) time and O(n) space for the counters. Discuss alternative approaches like checking the board after each move (O(n) per move) and why the counter method is superior.

Key Points to Mention

Use of row, column, and diagonal counters to achieve O(1) time per move.
Space complexity of O(n) for an n x n board, which is optimal for this approach.
Handling of both players by incrementing/decrementing counters (e.g., +1 for player 1, -1 for player 2).
Edge cases: invalid moves, moves after game ends, and draw detection.
Trade-offs: the counter method assumes a fixed board size and does not support undo easily; alternative is to check the board after each move.
Thread-safety considerations if the class is to be used in a concurrent environment.

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