Every short legal path from one position to a target placement

Searches all legal move sequences up to max_plies long and returns those that reach target_placement. Only the placement is compared, because that is all a screenshot can show - side to move, castling rights, en passant and the move clocks are not visible on a board and are instead carried forward by playing the moves.

Usage

find_move_paths(ctx, from_fen, target_placement, max_plies = 2L, cap = 4L)

Arguments

ctx

A chess.js V8 context from new_chess_context().

from_fen

The position we are confident about.

target_placement

The placement field just observed.

max_plies

Longest sequence to consider.

cap

Stop once this many distinct paths are found; the caller only needs to distinguish none, one and more-than-one.

Value

A list of character vectors of UCI moves, shortest first.

Details

Cost grows steeply with depth: two plies is around 1200 positions (~0.1s), three is around 40000 (~5s). Two is the useful setting - it covers a capture frame arriving only after the reply - and the default reflects that.