USING: arrays bit-arrays kernel math sequences sequences.extras
;
IN: 2025.07

: parse ( lines -- beams splitters-seq )
    [ [ CHAR: . = not ] ?{ } map-as ] map unclip swap ;

: split-beams ( n beams splitters -- n' beams' )
    [ [ length <bit-array> ] keep ] dip [
        spin [
            [
                t swap [ 1 - ] [ 1 + ] bi 2array pick set-nths
                [ 1 + ] dip
            ] [ t swap pick set-nth ] if
        ] [ 2drop ] if
    ] 2each-index ;

: part-1 ( beams splitters-seq -- n )
    [ 0 ] 2dip [ split-beams ] each drop ;

: find-splitter ( col row splitters-seq -- col row' )
    overd [ nth ] with find-from drop ;

MEMO: count-worlds ( col row splitters-seq -- n )
    [ find-splitter ] keep
    over [
        [ [ 1 - ] 2dip count-worlds ]
        [ [ 1 + ] 2dip count-worlds ] 3bi +
    ] [ 3drop 1 ] if ;

: part-2 ( beams splitters-seq -- n )
    [ t ] [ index 0 ] [ count-worlds ] tri* ;