Why chess tests polymorphism and strategy in LLD - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a base class for chess pieces.

LLD

class ChessPiece:
    def move(self, position):
        raise [1]Error("This method should be overridden")

Drag options to blanks, or click blank then click option'

ANotImplemented

BRuntime

CValue

DType

Attempts:

3 left

💡 Hint

Common Mistakes

Using RuntimeError instead of NotImplementedError

Forgetting to raise an error

The NotImplementedError is used to indicate that the method should be overridden in subclasses, which is key to polymorphism.

2fill in blank

medium

Complete the code to override the move method for the Knight piece.

LLD

class Knight(ChessPiece):
    def move(self, position):
        return "L-shaped move to " + [1]

Drag options to blanks, or click blank then click option'

Aself

Bposition

Cmove

Dposition()

Attempts:

3 left

💡 Hint

Common Mistakes

Using self instead of position

Calling position as a function

The position parameter holds the target position for the move, so it should be used directly.

3fill in blank

hard

Fix the error in the strategy pattern implementation for chess moves.

LLD

class MoveStrategy:
    def execute(self, piece, position):
        [1]

Drag options to blanks, or click blank then click option'

Araise NotImplementedError

Breturn piece.move(position)

Cpass

Dprint('Move executed')

Attempts:

3 left

💡 Hint

Common Mistakes

Using pass which does nothing

Returning a call without implementation

The base strategy should raise NotImplementedError to enforce implementation in subclasses.

4fill in blank

hard

Fill both blanks to implement a dictionary mapping piece names to their move strategies.

LLD

move_strategies = {
    'Knight': [1],
    'Bishop': [2]
}

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AKnightMoveStrategy()

BBishopMoveStrategy()

CPawnMoveStrategy()

DQueenMoveStrategy()

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up strategy classes

Using wrong piece names

Each chess piece is mapped to its corresponding move strategy instance to support polymorphic behavior.

5fill in blank

hard

Fill all three blanks to complete the function that selects and executes a move strategy based on piece type.

LLD

def execute_move(piece_type, position):
    strategy = move_strategies.get([1], [2])
    if strategy:
        return strategy.execute([3], position)
    else:
        return "Invalid piece type"

Drag options to blanks, or click blank then click option'

Apiece_type

BNone

Dposition

Attempts:

3 left

💡 Hint

Common Mistakes

Using position as dictionary key

Passing wrong arguments to execute

The function uses the piece_type to get the strategy, defaults to None if not found, and passes piece_type and position to execute.

Practice

1. In the context of chess and system design, what does polymorphism primarily demonstrate?

easy

A. Chess pieces cannot change their behavior during the game

B. Chess pieces all move in the same way regardless of type

C. Chess strategy is about random moves without planning

D. Different chess pieces use the same method name but have unique move behaviors

Solution

1. Step 1: Understand polymorphism in chess pieces

   Polymorphism means objects share the same interface but behave differently. Chess pieces all have a move method but move uniquely.

2. Step 2: Relate polymorphism to chess piece behavior

   Each piece type (pawn, knight, bishop) implements move differently, showing polymorphism.

3. Final Answer:

   Different chess pieces use the same method name but have unique move behaviors -> Option D

4. Quick Check:

   Polymorphism = Same method, different behavior [OK]

Hint: Polymorphism means same method, different actions [OK]

Common Mistakes:

• Thinking all pieces move the same way
• Confusing polymorphism with inheritance only
• Ignoring that method names are shared

2. Which of the following code snippets correctly shows polymorphism for chess pieces in a low-level design?

easy

A. class Piece { move() { /* generic move */ } } class Pawn extends Piece { move() { /* pawn move */ } }

B. class Pawn { move() { /* pawn move */ } } class Knight { jump() { /* knight jump */ } }

C. function move(piece) { if(piece.type == 'pawn') { /* move */ } else { /* no move */ } }

D. class Piece { move() { console.log('move'); } } let piece = new Piece(); piece.move();

Solution

1. Step 1: Identify polymorphism in code

   Polymorphism requires a base class with a method overridden by subclasses. class Piece { move() { /* generic move */ } } class Pawn extends Piece { move() { /* pawn move */ } } shows a base Piece class with move(), overridden by Pawn.

2. Step 2: Check other options for polymorphism

   class Pawn { move() { /* pawn move */ } } class Knight { jump() { /* knight jump */ } } lacks shared method names; function move(piece) { if(piece.type == 'pawn') { /* move */ } else { /* no move */ } } uses conditional logic, not polymorphism; class Piece { move() { console.log('move'); } } let piece = new Piece(); piece.move(); has no subclassing.

3. Final Answer:

   class Piece { move() { /* generic move */ } } class Pawn extends Piece { move() { /* pawn move */ } } -> Option A

4. Quick Check:

   Base class + overridden method = polymorphism [OK]

Hint: Look for base class with overridden methods [OK]

Common Mistakes:

• Confusing conditional logic with polymorphism
• Missing method overriding in subclasses
• Ignoring inheritance structure

3. Given the following pseudo-code, what will be the output when calling move() on each piece in the list?

class Piece { move() { return 'generic move'; } } class Knight extends Piece { move() { return 'L-shape move'; } } class Bishop extends Piece { move() { return 'diagonal move'; } } pieces = [new Piece(), new Knight(), new Bishop()] for p in pieces: print(p.move())

medium

A. L-shape move\ndiagonal move\ngeneric move

B. generic move\nL-shape move\ndiagonal move

C. generic move\ngeneric move\ngeneric move

D. Error: move method not found

Solution

1. Step 1: Understand method overriding in subclasses

   Each subclass overrides move() to return its specific move string.

2. Step 2: Trace the loop calling move()

   For Piece instance, move() returns 'generic move'. For Knight, 'L-shape move'. For Bishop, 'diagonal move'.

3. Final Answer:

   generic move\nL-shape move\ndiagonal move -> Option B

4. Quick Check:

   Overridden methods print their own strings [OK]

Hint: Each subclass method overrides base method output [OK]

Common Mistakes:

• Assuming base method output for all pieces
• Mixing order of outputs
• Expecting runtime errors incorrectly

4. Identify the error in this chess piece design code snippet:

class Piece { move() { throw 'Not implemented'; } } class Queen extends Piece { } let q = new Queen(); q.move();

medium

A. Queen class should not inherit from Piece

B. Piece class should not have a move() method

C. Queen class does not override move(), causing runtime error

D. No error, code runs fine

Solution

1. Step 1: Analyze base class move() method

   Piece.move() throws an error if called directly, indicating it must be overridden.

2. Step 2: Check Queen class implementation

   Queen does not override move(), so calling q.move() calls base method and throws error.

3. Final Answer:

   Queen class does not override move(), causing runtime error -> Option C

4. Quick Check:

   Abstract method not overridden = runtime error [OK]

Hint: Abstract methods must be overridden to avoid errors [OK]

Common Mistakes:

• Assuming base method runs without error
• Thinking inheritance is wrong here
• Ignoring the throw statement in base method

5. How does combining polymorphism and strategy in chess help design a flexible and smart system?

hard

A. Polymorphism allows different piece behaviors; strategy plans moves ahead for better decisions

B. Polymorphism forces all pieces to behave identically; strategy ignores future moves

C. Strategy replaces polymorphism by hardcoding moves; polymorphism is unnecessary

D. Polymorphism and strategy are unrelated concepts in system design

Solution

1. Step 1: Understand polymorphism's role in flexibility

   Polymorphism lets different pieces share an interface but act differently, enabling flexible design.

2. Step 2: Understand strategy's role in smart planning

   Strategy involves planning moves ahead to make smart decisions, improving system intelligence.

3. Step 3: Combine both concepts

   Together, polymorphism provides flexible behaviors, and strategy guides smart choices, creating a robust system.

4. Final Answer:

   Polymorphism allows different piece behaviors; strategy plans moves ahead for better decisions -> Option A

5. Quick Check:

   Polymorphism + strategy = flexible, smart system [OK]

Hint: Polymorphism = flexibility; strategy = planning [OK]

Common Mistakes:

• Thinking polymorphism means identical behavior
• Ignoring the importance of planning in strategy
• Separating polymorphism and strategy as unrelated