Special moves (castling, en passant) in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Castling Conditions

Which of the following is NOT a valid condition for castling in chess?

A The king is currently in check.

B There are no pieces between the king and the rook.

C Neither the king nor the rook involved has moved before.

D The squares the king passes over are not under attack.

💡 Hint

Think about whether the king can castle while in check.

Castling is not allowed if the king is currently in check. The other conditions must be met for castling to be valid.

❓ Architecture

intermediate

Designing En Passant Detection

In designing a chess game system, which component is most responsible for detecting the possibility of an en passant move?

A The piece movement module that only moves pieces without validation.

B The user interface module that highlights possible moves.

C The game timer module that tracks player time.

D The move validation module that checks the last move and current board state.

💡 Hint

Consider which part knows about the last move and rules.

The move validation module must check if the last move was a two-square pawn advance and if an en passant capture is possible.

❓ scaling

advanced

Scaling a Chess Engine for Multiple Games

You are designing a server to handle thousands of simultaneous chess games including special moves like castling and en passant. Which approach best ensures consistent game state and move validation?

A Store game states in a distributed cache without locking mechanisms.

B Allow clients to validate moves locally and send updates without server checks.

C Use a centralized game state service with atomic transactions for each move validation and update.

D Process moves asynchronously without immediate validation to improve throughput.

💡 Hint

Think about consistency and correctness under load.

A centralized service with atomic transactions ensures moves are validated correctly and game state remains consistent, especially for special moves requiring strict rules.

❓ tradeoff

advanced

Tradeoffs in Representing Castling Rights

Which data structure choice best balances memory efficiency and clarity when tracking castling rights in a chess game system?

A Use four boolean flags indicating castling availability for each rook and king side.

B Use a single integer bitmask where each bit represents a castling right.

C Store castling rights as a string describing allowed moves (e.g., "KQkq").

D Maintain a list of moves that have occurred to infer castling rights dynamically.

💡 Hint

Consider compactness and ease of checking rights.

A bitmask uses minimal memory and allows fast bitwise operations to check castling rights, balancing efficiency and clarity.

❓ estimation

expert

Estimating Storage for Game History with Special Moves

Estimate the approximate storage size needed to store the full move history of 1 million chess games including special moves like castling and en passant, assuming each move is stored as a 4-byte record. Average moves per game is 80.

A Approximately 320 MB

B Approximately 80 MB

C Approximately 3.2 GB

D Approximately 800 MB

💡 Hint

Calculate total moves and multiply by bytes per move.

1,000,000 games * 80 moves/game = 80,000,000 moves. 80,000,000 moves * 4 bytes = 320,000,000 bytes = 320 MB.