Object-Oriented Design of a Chess Game with Full Move Legality

Design a chess game. The report gives only this one-line prompt, so settle the scope with the interviewer first. In its usual object-oriented form: model the board, the pieces, the players and the moves so that two players can play a complete game, every move is checked against the rules of chess, and the program knows when and how the game has ended. ```hint Where does move logic live Decide which object knows how a piece may move and which object knows whether a move is legal in the current position; they are not the same question. ``` ```hint Reachable is not the same as legal A move that a piece can geometrically make may still be illegal. Think about which rule causes that, and how to check it without duplicating movement logic. ``` ### Constraints and Clarifications - Not given: the interface (console, graphical, networked), whether there is a computer opponent or a clock, and which draw rules must be enforced. Ask, or state your assumptions. ### Clarifying Questions - Is the goal an object model for the game logic, or an online service where players are matched and play over the network? - Two people on one device, or also a computer opponent? Is there a clock? - Which rules must be enforced: castling, en passant and promotion; check, checkmate and stalemate; draws by repetition or the fifty-move rule? - Must the game support undo, saving and loading, or replaying a game from its move list? ### What a Strong Answer Covers - Settles the scope (local model or online service, opponents, clock, rule set) before designing - A cohesive class model: game, board and squares, pieces, players, moves and move history - Clean separation of piece movement patterns from position-level legality (never leaving one's own king in check) - Special moves and the state they need: castling rights, the en passant square, promotion - End-of-game detection: checkmate, stalemate, resignation and the agreed draw rules - Extensibility and testability: undo, replay, variants, and tests for each rule ### Follow-up Questions - How would you implement undo, and what must each move record so that undo is exact? - How would you add a chess clock, or a variant with different piece rules, without rewriting the core? - How would you detect a draw by threefold repetition efficiently? - If the two players play online, what changes, and which component decides whether a move is legal?