Board, Player, Game classes in LLD - Architecture Diagram

System Overview - Board, Player, Game classes

This system models a simple turn-based game using three main classes: Board, Player, and Game. The Board represents the playing area, Player holds player details and actions, and Game manages the game flow and rules.

Architecture Diagram

  +---------+       +---------+       +-------+
  |  Player | <---> |   Game  | <---> | Board |
  +---------+       +---------+       +-------+

Components

Player

class

Represents a participant in the game with identity and actions

Game

class

Controls game logic, turn management, and interaction between players and board

Board

class

Represents the game state and playing area where moves are made

Request Flow - 4 Hops

Player → Game

Game → Board

Board → Game

Game → Player

Failure Scenario

Component Fails:Board

Impact:Game cannot update or validate moves, causing game flow to halt

Mitigation:Implement error handling in Game to notify players and possibly reset or reload board state

Architecture Quiz - 3 Questions

Which class is responsible for managing the game rules and turn order?

A Board

B Game

C Player

D None of the above

Design Principle

This design cleanly separates concerns: Player handles user identity and actions, Board manages game state, and Game orchestrates the flow and rules. This modular approach simplifies maintenance and testing.

Practice

1. Which class is primarily responsible for keeping track of the current state of the game board in a typical game design involving Board, Player, and Game classes?

easy

A. Score class

B. Player class

C. Game class

D. Board class

Solution

1. Step 1: Understand the role of the Board class

   The Board class holds the layout and current state of the game, such as positions of pieces or marks.

2. Step 2: Compare with Player and Game classes

   The Player class stores player details, and the Game class manages turns and rules, not the board state.

3. Final Answer:

   Board class -> Option D

4. Quick Check:

   Board = game state holder [OK]

Hint: Board holds game state, Player holds info, Game controls flow [OK]

Common Mistakes:

• Confusing Player with Board for state storage
• Thinking Game class stores board state
• Assuming Score class manages board

2. Which of the following is the correct way to define a Player class constructor that stores a player's name and ID in a typical object-oriented design?

easy

A. class Player { constructor(name, id) { this.name = name; this.id = id; } }

B. class Player { Player(name, id) { this.name = name; this.id = id; } }

C. function Player(name, id) { this.name = name; this.id = id; }

D. class Player { def __init__(self, name, id): self.name = name; self.id = id }

Solution

1. Step 1: Identify the correct constructor syntax in JavaScript

   In JavaScript ES6+, the constructor method inside a class is named constructor.

2. Step 2: Check other options for errors

   class Player { Player(name, id) { this.name = name; this.id = id; } } uses a method named Player instead of constructor; function Player(name, id) { this.name = name; this.id = id; } is a function, not a class; class Player { def __init__(self, name, id): self.name = name; self.id = id } uses Python syntax.

3. Final Answer:

   class Player { constructor(name, id) { this.name = name; this.id = id; } } -> Option A

4. Quick Check:

   JavaScript class constructor = constructor() [OK]

Hint: JS class constructors use 'constructor' keyword [OK]

Common Mistakes:

• Using method named same as class instead of constructor
• Mixing Python syntax in JavaScript
• Defining constructor as a separate function

3. Given the following simplified code snippet, what will be the output after calling game.playTurn() once?

class Player {
  constructor(name) { this.name = name; }
}
class Board {
  constructor() { this.state = ['-', '-', '-']; }
  mark(position, symbol) { this.state[position] = symbol; }
}
class Game {
  constructor() {
    this.board = new Board();
    this.players = [new Player('Alice'), new Player('Bob')];
    this.currentPlayerIndex = 0;
  }
  playTurn() {
    const player = this.players[this.currentPlayerIndex];
    this.board.mark(0, this.currentPlayerIndex === 0 ? 'X' : 'O');
    this.currentPlayerIndex = 1 - this.currentPlayerIndex;
    return this.board.state;
  }
}
const game = new Game();
console.log(game.playTurn());

medium

A. ['X', '-', '-']

B. ['O', '-', '-']

C. ['-', '-', '-']

D. Error: mark method not found

Solution

1. Step 1: Analyze initial state and playTurn logic

   Board state starts as ['-', '-', '-']. Current player index is 0, so symbol 'X' is placed at position 0.

2. Step 2: Update currentPlayerIndex and return state

   After marking, currentPlayerIndex switches to 1. The returned board state is ['X', '-', '-'].

3. Final Answer:

   ['X', '-', '-'] -> Option A

4. Quick Check:

   First turn marks 'X' at position 0 [OK]

Hint: First player marks 'X' at position 0 on first turn [OK]

Common Mistakes:

• Assuming 'O' is placed first
• Not updating currentPlayerIndex
• Confusing board state initialization

4. In the following code snippet, what is the main issue that will cause the game to not switch players correctly?

class Game {
  constructor() {
    this.players = ['Alice', 'Bob'];
    this.currentPlayerIndex = 0;
  }
  nextTurn() {
    this.currentPlayerIndex += 1;
    if (this.currentPlayerIndex > this.players.length) {
      this.currentPlayerIndex = 0;
    }
  }
}

medium

A. Players array should contain Player objects, not strings

B. The condition should be >= players.length, not >

C. currentPlayerIndex should start at 1, not 0

D. nextTurn method should decrement currentPlayerIndex

Solution

1. Step 1: Understand player index bounds

   Array indices go from 0 to length-1. If currentPlayerIndex equals players.length, it is out of bounds.

2. Step 2: Check condition for resetting index

   The condition uses > players.length, which misses the case when currentPlayerIndex == players.length, causing an error.

3. Final Answer:

   The condition should be >= players.length, not > -> Option B

4. Quick Check:

   Index reset condition must include equality [OK]

Hint: Check array index bounds carefully for off-by-one errors [OK]

Common Mistakes:

• Using > instead of >= for index reset
• Ignoring zero-based indexing
• Thinking player array type causes index error

5. You want to design a turn-based game system using Board, Player, and Game classes. Which design choice best supports adding new game rules and multiple player types (e.g., human, AI) without changing existing code much?

hard

A. Use global variables for player types and rules to simplify access

B. Keep all logic inside Game class and add if-else for player types and rules

C. Use inheritance: create subclasses like HumanPlayer and AIPlayer from Player, and extend Game with rule classes

D. Store all player and rule info in Board class to centralize state

Solution

1. Step 1: Consider extensibility and separation of concerns

   Inheritance allows creating specialized Player types without modifying base Player class, supporting new behaviors.

2. Step 2: Use modular design for rules

   Extending Game with separate rule classes or modules keeps code clean and easy to maintain.

3. Final Answer:

   Use inheritance: create subclasses like HumanPlayer and AIPlayer from Player, and extend Game with rule classes -> Option C

4. Quick Check:

   Inheritance and modular rules = easy extension [OK]

Hint: Use inheritance and modular rules for easy feature addition [OK]

Common Mistakes:

• Putting all logic in one class causing messy code
• Using global variables leading to hard-to-maintain code
• Storing rules in Board instead of Game