Board, Player, Game classes in LLD - System Design Exercise

Design: Turn-based Game System

Design classes for Board, Player, and Game to manage game logic and state. UI, network communication, and persistence are out of scope.

Functional Requirements

FR1: Support multiple players in a game

FR2: Manage the game board state

FR3: Allow players to take turns making moves

FR4: Track player scores and game progress

FR5: Detect game end conditions (win, draw, etc.)

Non-Functional Requirements

NFR1: Support up to 4 players per game

NFR2: Each move must be processed within 100ms

NFR3: System should be designed for easy extension to different game types

NFR4: Maintain game state consistency during concurrent player actions

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Board class to represent game state

Player class to represent each participant

Game class to manage game flow and rules

Design Patterns

State pattern for managing game phases

Observer pattern for notifying players of state changes

Command pattern for encapsulating player moves

Reference Architecture

  +----------------+       +----------------+       +----------------+
  |    Player      |<----->|     Game       |<----->|     Board      |
  +----------------+       +----------------+       +----------------+
         ^                        ^                        ^
         |                        |                        |
  playerId, name           gameId, players          boardState, size
  score, status            currentTurn, status      update(), reset()

Components

Player

Class

Represents a player with identity, score, and status in the game

Board

Class

Maintains the current state of the game board and provides methods to update and query it

Game

Class

Controls game flow, manages players and board, enforces rules, and tracks game progress

Request Flow

1. 1. Game initializes Board and Player instances.

2. 2. Game sets the first player's turn.

3. 3. Player makes a move by invoking Game's move method.

4. 4. Game validates the move and updates Board state.

5. 5. Game updates Player scores and checks for end conditions.

6. 6. Game switches turn to the next Player.

7. 7. Repeat steps 3-6 until game ends.

Database Schema

Entities: - Player: player_id (PK), name, score, status - Game: game_id (PK), current_turn (FK to Player), status - Board: board_id (PK), game_id (FK to Game), state (serialized board data) Relationships: - Game has many Players - Game has one Board - Player participates in many Games (if multiplayer across sessions)

Scaling Discussion

Bottlenecks

Handling concurrent moves from multiple players

Maintaining consistent game state under concurrent access

Extending to support multiple simultaneous games

Solutions

Use locking or transactional mechanisms to serialize moves per game instance

Implement optimistic concurrency control with versioning for board state

Design Game instances to be independent and scalable horizontally

Interview Tips

Time: Spend 10 minutes clarifying requirements and scope, 20 minutes designing classes and interactions, 10 minutes discussing scaling and improvements, 5 minutes for questions.

Explain clear separation of concerns between Board, Player, and Game classes

Discuss how turns and moves are managed to ensure fairness and consistency

Highlight extensibility for different game types and rules

Address concurrency and state consistency challenges

Mention design patterns that improve maintainability and flexibility