Piece movement rules (polymorphism) in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is polymorphism in the context of piece movement rules in a board game?

Polymorphism allows different piece types to have their own movement rules by using a common interface or base class. Each piece class implements its own version of the move method.

intermediate

Why use polymorphism for piece movement rules instead of a large conditional statement?

Polymorphism makes the code cleaner, easier to maintain, and extend. Adding new pieces requires creating new classes without changing existing code, following the Open/Closed Principle.

beginner

How does a base class or interface help in implementing piece movement rules?

A base class or interface defines a common method like move(). Each piece class overrides this method to provide its specific movement logic.

intermediate

Give an example of how polymorphism can simplify checking valid moves for different pieces.

Instead of checking piece type with if-else, call piece.move(). Each piece knows how to validate its moves, so the game engine just calls the method without caring about piece type.

advanced

What design pattern is commonly used with polymorphism for piece movement rules?

The Strategy pattern is often used, where each piece’s movement logic is encapsulated in a separate class implementing a common interface.

What does polymorphism allow in piece movement rules?

A Movement rules are hardcoded in one place

B All pieces share the same movement logic

C Different pieces implement their own move logic using a common method

D Pieces cannot move

Polymorphism lets each piece class implement its own move method, enabling different movement rules.

Which principle is followed by using polymorphism for piece movement rules?

A Open/Closed Principle

B Single Responsibility Principle

C Don’t Repeat Yourself

D YAGNI

Polymorphism allows adding new pieces without modifying existing code, following the Open/Closed Principle.

What is the role of a base class or interface in polymorphic piece movement?

A Handles user input

B Stores the board state

C Draws the pieces

D Defines a common move method to be overridden

The base class or interface defines the move method that each piece class overrides with its own logic.

Which design pattern is often used with polymorphism for piece movement?

A Strategy

B Singleton

C Observer

D Factory

The Strategy pattern encapsulates movement logic in separate classes, used with polymorphism.

What is a key benefit of using polymorphism for piece movement rules?

A Faster execution speed

B Easier to add new piece types without changing existing code

C Less memory usage

D No need for classes

Polymorphism supports extensibility by allowing new pieces to be added without modifying existing code.

Explain how polymorphism helps implement piece movement rules in a board game system.

Think about how different pieces move differently but share a common method.

Describe the advantages of using polymorphism over if-else statements for piece movement logic.

Consider maintainability and scalability benefits.

Practice

1. What is the main benefit of using polymorphism for piece movement rules in a game design?

easy

A. It allows each piece to have its own move logic without type checks.

B. It forces all pieces to share the same move logic.

C. It requires manual checking of piece types before moving.

D. It prevents pieces from moving on the board.

Solution

1. Step 1: Understand polymorphism concept

   Polymorphism allows different objects to be treated through a common interface while having their own behavior.

2. Step 2: Apply to piece movement

   Each piece class implements its own move() method, so no need to check piece type before moving.

3. Final Answer:

   It allows each piece to have its own move logic without type checks. -> Option A

4. Quick Check:

   Polymorphism = own move logic without type checks [OK]

Hint: Polymorphism means no type checks for moves [OK]

Common Mistakes:

• Thinking all pieces share the same move logic
• Believing manual type checks are needed
• Confusing polymorphism with inheritance only

2. Which of the following is the correct way to declare a base class method for piece movement in a polymorphic design?

easy

A. move(self): pass

B. def move(self): pass

C. def move(): pass

D. def move(self, board): return

Solution

1. Step 1: Recall method declaration syntax in Python

   Instance methods must have self as the first parameter.

2. Step 2: Identify correct method signature

   def move(self): pass correctly declares a method with self and no implementation.

3. Final Answer:

   def move(self): pass -> Option B

4. Quick Check:

   Method with self parameter = def move(self): pass [OK]

Hint: Instance methods always start with self parameter [OK]

Common Mistakes:

• Omitting self parameter in method
• Using incorrect syntax without def keyword
• Adding unnecessary parameters without context

3. Given the following code, what will be the output?

class Piece:
    def move(self):
        return "Base move"

class Knight(Piece):
    def move(self):
        return "L-shaped move"

pieces = [Piece(), Knight()]
for p in pieces:
    print(p.move())

medium

A. Base move\nL-shaped move

B. L-shaped move\nL-shaped move

C. Error: move() not implemented

D. Base move\nBase move

Solution

1. Step 1: Understand method overriding

   Subclass Knight overrides move() to return "L-shaped move".

2. Step 2: Trace the loop output

   First object is Piece, prints "Base move"; second is Knight, prints "L-shaped move".

3. Final Answer:

   Base move\nL-shaped move -> Option A

4. Quick Check:

   Base class and overridden subclass moves printed [OK]

Hint: Subclass method overrides base method output [OK]

Common Mistakes:

• Assuming base method always runs
• Expecting same output for all pieces
• Confusing method overriding with overloading

4. Identify the error in the following polymorphic piece movement code:

class Piece:
    def move(self):
        pass

class Bishop(Piece):
    def move():
        print("Diagonal move")

b = Bishop()
b.move()

medium

A. Cannot instantiate Bishop directly

B. Piece.move() should return a value

C. Bishop.move() missing self parameter

D. print statement syntax error

Solution

1. Step 1: Check method signatures

   Bishop.move() lacks self parameter, so it is not a proper instance method.

2. Step 2: Understand call context

   Calling b.move() passes self automatically, causing a TypeError due to missing parameter.

3. Final Answer:

   Bishop.move() missing self parameter -> Option C

4. Quick Check:

   Instance methods must have self parameter [OK]

Hint: Instance methods always need self parameter [OK]

Common Mistakes:

• Ignoring missing self in subclass method
• Thinking base class method must return value
• Assuming print syntax is wrong

5. You are designing a chess game using polymorphism for piece movement. How should you structure your classes to allow easy addition of new piece types without changing existing code?

hard

A. Write a single move() function with if-else for each piece type.

B. Implement move logic only in the base class and override rarely.

C. Use global variables to track piece types and moves.

D. Create a base Piece class with an abstract move() method; each piece subclass implements move().

Solution

1. Step 1: Apply polymorphism design principle

   Use a base class with an abstract or empty move() method to define interface.

2. Step 2: Implement subclasses for each piece

   Each piece subclass provides its own move() logic, enabling extension without modifying base code.

3. Final Answer:

   Create a base Piece class with an abstract move() method; each piece subclass implements move(). -> Option D

4. Quick Check:

   Base class + subclass move() = scalable design [OK]

Hint: Base class with abstract move() enables easy extension [OK]

Common Mistakes:

• Using if-else instead of polymorphism
• Relying on global variables for logic
• Putting all move logic in base class only