FA-82823 / Chess move legality / Member archive

Moved piece left behind on its origin · case 03

A knight that moved from g1 can move from g1 again.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input: {"board", "turn": "w" or "b", "moves": [[from, to], ...]}. Replay the moves; return the index of the first move that starts from an empty square, moves a piece of the side not to move, or lands on a piece of its own colour; return -1 if all pass. Each move replaces any piece on the destination and passes the turn.

Why this case matters

Game servers must reject out-of-turn and self-capturing moves in submitted move lists.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
vacated square reused	`-1`	`2`	Failed

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