Design Snake and Ladder

Board, dice, snakes, ladders, and player positions.

Expert13 min read

Read these first

Design Tic-Tac-Toe

Why this matters

Board with cells 1–100
Scope — what "Board cells" covers inside Snake and Ladder and what it does not
Scope — what "Dice" covers inside Snake and Ladder and what it does not
Scope — what "Game loop" covers inside Snake and Ladder and what it does not
Games and architecture patterns signal staff+ depth.

Waiting

InProgress

Finished

Turn-based games map cleanly to State pattern — one handler per game phase.

CampusOS context

CampusOS is the fictional smart-campus platform used across this track. Treat this module as a real product slice:

Context

Belongs to CampusOS — same naming and design vocabulary as parking, library, and booking modules
Scope is one JVM — persistence is in-memory or behind a repository interface
Goal is a class diagram + core Java that an interviewer can follow in 35–45 minutes
Extension paragraph at the end links to System Design when scale exceeds one process

Requirements snapshot

Functional requirements

Board with cells 1–100
Snakes move player down; ladders move up
Dice roll 1–6; move token accordingly
First to cell 100 wins
Multiple players take turns

Non-functional requirements

Single JVM, in-process design for this LLD article
Core flows testable with in-memory repositories
Extension points for new rules without editing central god classes
Clear public API on facade/service layer
CampusOS extension links to System Design when scale demands distribution

Overview

This CampusOS module designs Snake and Ladder as a production-ready in-process service. Read requirements point-by-point before drawing classes.

Requirements

Points to cover

Board with cells 1–100
Snakes move player down; ladders move up
Dice roll 1–6; move token accordingly
First to cell 100 wins
Multiple players take turns

Board cells

Points to cover

Scope — what "Board cells" covers inside Snake and Ladder and what it does not
Classes — name 2–4 classes/interfaces responsible for this slice
Flow — step-by-step: trigger → validation → state change → side effect
Edge cases — invalid input, concurrent access, empty state, timeout
Pattern — Strategy, State, Observer, or Facade if it fits naturally
Test hook — one scenario an interviewer will ask you to walk through

Dice

Points to cover

Scope — what "Dice" covers inside Snake and Ladder and what it does not
Classes — name 2–4 classes/interfaces responsible for this slice
Flow — step-by-step: trigger → validation → state change → side effect
Edge cases — invalid input, concurrent access, empty state, timeout
Pattern — Strategy, State, Observer, or Facade if it fits naturally
Test hook — one scenario an interviewer will ask you to walk through

Game loop

Points to cover

Scope — what "Game loop" covers inside Snake and Ladder and what it does not
Classes — name 2–4 classes/interfaces responsible for this slice
Flow — step-by-step: trigger → validation → state change → side effect
Edge cases — invalid input, concurrent access, empty state, timeout
Pattern — Strategy, State, Observer, or Facade if it fits naturally
Test hook — one scenario an interviewer will ask you to walk through

Java

// CampusOS — SnakeAndLadder facade (keep thin)
public final class SnakeAndLadderService {
    private final SnakeAndLadderRepository repository;

    public SnakeAndLadderService(SnakeAndLadderRepository repository) {
        this.repository = repository;
    }

    /** Orchestrate: validate → domain rules → persist → return result */
    public Result handle(Request request) {
        request.validate();
        var domain = DomainModel.from(request);
        domain.applyRules();
        return repository.save(domain);
    }
}

Quick recall

Everything you need if you only revisit this box.

Requirements — review this slice before mock interviews.
Board cells — review this slice before mock interviews.
Dice — review this slice before mock interviews.
Game loop — review this slice before mock interviews.

CampusOS extension

When this outgrows one JVM

Shard inventory or state by campus ID or geographic region
Push notifications, payments, and search to dedicated services (System Design track)
Use message queues for async side effects (email, analytics)
The class diagram you drew here becomes one box on the HLD architecture diagram

Test yourself

Answer these before moving on — recall is what makes it stick.