Databricks·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say

Apr 2026Remote

Summary

Databricks coding round focused on a generalized tic-tac-toe problem. The DSU angle was the interesting part and I didn't see it coming at first.

Questions Asked (1)

Design and implement a generalized m×n board game where two players alternate placing marks, and after each move you need to efficiently check if the current player has formed a connected line of k marks in any direction (horizontal, vertical, or diagonal). Implement a move(row, col, player) method that returns whether the move results in a win.

Algorithms & Data StructuresSystem DesignTechnical Trade-offs

Author's notes

My first instinct was the naive scan approach, check all four directions from the placed cell and count.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints (board size, k, win condition) and then propose an efficient solution that checks only around the last move. Use directional scanning from the placed mark to count consecutive marks in all 8 directions, leveraging symmetry to reduce checks. Discuss trade-offs between time and space, and consider edge cases like k=1 or board boundaries.

Pro tip: Emphasize that checking only the last move is sufficient because a win can only be formed by the newly placed mark; this reduces the check from O(m*n) to O(k) per move. Also, mention that you can optimize by storing counts per direction or using a union-find structure for dynamic connectivity if the game allows moves to be undone.

1. Clarify requirements and constraints

Ask about board dimensions, k value, win condition (exactly k or at least k), and whether moves can be undone. Confirm that a win is only possible after a move and that the board may be large.

2. Design the data structure

Choose a representation for the board (e.g., 2D array) and decide how to track moves. Consider if additional structures like union-find or direction-specific counters are needed for efficiency.

3. Implement the move and win check

For each move, place the mark and then check for a win by scanning in all 8 directions from the placed mark, counting consecutive marks of the same player. Use symmetry to avoid redundant checks (e.g., only check 4 directions and their opposites).

4. Analyze complexity and trade-offs

Explain that the win check is O(k) time and O(1) extra space, which is optimal since you must examine at least k cells. Discuss alternatives like precomputing lines or using union-find for O(alpha(n)) per move but with higher constant factors.

5. Handle edge cases and test

Consider cases like k=1 (immediate win), k > board dimensions (impossible), moves at edges, and multiple wins. Write tests to verify correctness and performance.

Key Points to Mention

Only the last move can create a win, so checking around it is sufficient and efficient.
Directional scanning: check 4 axes (horizontal, vertical, two diagonals) by counting in both directions from the move.
Time complexity: O(k) per move, space O(m*n) for board or O(1) extra if board is given.
Trade-offs: union-find for dynamic connectivity gives faster amortized checks but more complex and higher memory.
Edge cases: k=1, k larger than board, moves at boundaries, and multiple winning lines.
Optimization: early termination when count reaches k, and using symmetry to halve the number of direction checks.

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