FA-82778 / Chess move legality / Member archive

Every position without king moves called checkmate · case 03

A cornered black king that is not in check is declared mated.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input: {"wk", "wq", "bk"} squares, black to move. Return "checkmate" if black has no legal king move and is attacked by the queen, "stalemate" if it has none and is not attacked, else "ongoing". The queen attacks along ranks, files and diagonals and is blocked only by the white king; the black king may capture the queen when it is not adjacent to the white king.

Why this case matters

Game-end detection must distinguish mate from stalemate exactly.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
corner stalemate	`"checkmate"`	`"stalemate"`	Failed

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