Board, Player, Game classes in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main responsibility of the <strong>Board</strong> class in a game design?

The Board class manages the game area or playing field. It keeps track of the state of each position or cell on the board, such as which player occupies it or if it is empty.

beginner

What does the <strong>Player</strong> class typically represent in a game system?

The Player class represents a participant in the game. It stores player-specific information like name, ID, score, and may include methods to make moves or interact with the game.

intermediate

How does the <strong>Game</strong> class coordinate the Board and Player classes?

The Game class acts as the controller. It initializes the Board and Players, manages the game flow, enforces rules, and determines the game outcome by interacting with Board and Player objects.

intermediate

Why is it important to separate concerns between Board, Player, and Game classes?

Separating concerns makes the design modular and easier to maintain. Each class has a clear role, reducing complexity and allowing independent updates or testing without affecting others.

beginner

Give an example of a method you might find in the Game class.

A method like startGame() to initialize players and board, or makeMove(player, position) to process a player's move and update the board state.

Which class is responsible for storing the current state of the game board?

A Board

B Player

C Game

D Controller

The Board class stores and manages the current state of the game board.

Which class typically holds information like player name and score?

A UI

B Board

C Game

D Player

The Player class holds player-specific information such as name and score.

What is the main role of the Game class?

A Store player data

B Manage game flow and rules

C Display the game board

D Save game history

The Game class manages the game flow, enforces rules, and coordinates between Board and Player.

Why should Board, Player, and Game be separate classes?

A To keep responsibilities clear and modular

B To confuse developers

C To make the code longer

D To reduce performance

Separating classes keeps responsibilities clear and makes the system modular and maintainable.

Which method would you expect in the Game class?

A updateScore() in Player

B resetBoard() in Board

C startGame() in Game

D drawPiece() in Player

startGame() is a typical method in the Game class to begin the game.

Explain the roles of Board, Player, and Game classes in a simple game design.

Think about who manages the playing field, who represents the participants, and who runs the game.

Describe why separating Board, Player, and Game into different classes helps in software design.

Consider how dividing tasks helps keep code organized and flexible.

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