Design connect four
PremiumMachine codingEasy
- Win detection
- Grid games
- Gravity drop
Quick answer
This machine coding interview question asks you to design connect four. Aim for a design that meets its requirements at the stated scale, then explain its main components, data flow and trade-offs. Interviewers want to see how you scope the problem, size it and defend each choice.
The problem
Build Connect Four as a game engine: two players take turns dropping discs into a 7-column, 6-row grid, and each disc falls to the lowest empty cell. The first to line up four in a row across, up or diagonally wins. The hard parts are checking wins cheaply from the last move and keeping rules apart from input and printing.
What must the system do?
- New game: new Game(cols = 7, rows = 6, connect = 4) with players RED and YELLOW; RED moves first. A connect length larger than both sides is rejected.
- Drop: drop(col) puts the current player's disc in the lowest empty cell of column col (0-based) and returns its row, or throws for a full column, a column out of range or a move after the game is over.
How well must it do it?
- Cheap win check: A drop is checked in O(connect) steps around the new disc, not by scanning the board.
- O(1) drop: Keep the height of each column so a drop never searches the column.
What scale should you design for?
Use these numbers in your estimates.
The scale numbers unlock with this questionUnlock
Key concepts
- Win detection
- Grid games
- Gravity drop
- Game state
- Bitboards
- Unit testing
How you’ll practise
- Requirements
- Entities and interfaces
- Core implementation
- Edge cases and tests
- Extensions
- Wrap-up
Lala, personalized to you, gives a hint when you ask and reviews your design when you are ready.
What do interviewers look for?
In any machine coding design round.
- Clarifies the requirements before drawing anything
- Uses a few numbers that actually change the design
- Draws a clear path from the client to storage
- Picks storage and caching with reasons, not by habit
- Explains what breaks first under load and how to fix it
- States trade-offs openly instead of claiming a perfect design
Questions people ask about this interview question
- Which design type is this question?
- It is a machine coding question. You design connect four and explain your choices the way you would in an interview.
- Is this question asked at entry level?
- It is marked Easy, so it suits engineers who are new to machine coding interviews. It is also a good warm-up before harder questions.
- What should I cover first?
- Start with the requirements: what the system must do, how well it must do it and which numbers change the design. Agree on scope with the interviewer before you design anything.
- Can I practise it for free?
- It is a premium question. Sign up and unlock it once for 10 credits; it then stays unlocked. When you finish, Lala, your personalized AI mentor, can review your design for 30 credits.
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Updated · Written by the SevyDevy team