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Early-stage Startup·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Coding interview for a software engineer role, basically just one question about implementing Tic-Tac-Toe from scratch. Pretty self-contained but there are more edge cases than you'd expect.

Questions Asked (1)

Q1

Implement a Tic-Tac-Toe class with methods to make a move (validating it), check for a winner, and display the board.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Looks easy until you start thinking about all the ways make_move can fail.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then design a clean class structure with a 2D array or 1D list for the board. Implement move validation, win detection, and display methods, discussing trade-offs and edge cases as you go.

Pro tip: Mention that you'd separate the core game logic from the display to make it testable and adaptable for different UIs (CLI, web, etc.). This shows foresight and good design principles.

1. Clarify Requirements

Ask about board size (standard 3x3?), number of players, win conditions, and whether the game supports undo or reset. Confirm input/output expectations.

2. Design the Class

Define the class with a board representation (e.g., 2D array of chars), current player, and methods: makeMove(row, col), checkWinner(), displayBoard(). Consider using an enum for cell states.

3. Implement Move Validation

In makeMove, check if the game is already won, if the cell is empty, and if the coordinates are within bounds. Throw exceptions or return booleans for invalid moves.

4. Implement Win Detection

After each move, check rows, columns, and diagonals for three in a row. Optimize by only checking lines through the last move, and handle draw conditions.

5. Implement Display and Discuss Trade-offs

Write a simple display method that prints the board. Discuss trade-offs: 2D vs 1D array, early win detection vs full board scan, and extensibility for larger boards.

Key Points to Mention

  • Board representation: 2D array vs 1D array with index math, and why you chose one.
  • Move validation: bounds checking, cell occupancy, and game state (won/draw).
  • Win detection algorithm: checking rows, columns, diagonals; optimizing by checking only lines through the last move.
  • Draw condition: board full and no winner.
  • Separation of concerns: game logic vs display, making it testable and UI-agnostic.
  • Extensibility: supporting different board sizes or win lengths (e.g., 4x4 with 4 in a row).

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