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#lang br
( require racket/file sugar rackunit racket/set racket/bool )
( define links ( for/set ( [ line ( file->lines " 12.rktd " ) ] )
( list->set ( string-split line " - " ) ) ) )
( define ( is-downcase? loc ) ( equal? ( string-downcase loc ) ) )
( define ( paths-from last-loc links [ small-caves ( set ) ] )
( match last-loc
[ " end " ' ( ( " end " ) ) ]
[ loc #:when ( and small-caves ( set-member? small-caves loc ) )
( define pruned-links
( for*/set ( [ previous-locs ( in-value ( set-remove small-caves loc ) ) ]
[ link links ]
#:when ( set-empty? ( set-intersect link previous-locs ) ) )
link ) )
( paths-from last-loc pruned-links #false ) ]
[ loc
( define next-lc-visited ( cond
[ ( false? small-caves ) #false ]
[ ( and ( is-downcase? loc ) ( not ( equal? loc " start " ) ) )
( set-add small-caves loc ) ]
[ else small-caves ] ) )
( define links-with-loc ( for/set ( [ link links ]
#:when ( set-member? link loc ) )
link ) )
( define remaining-links ( if ( or ( equal? loc " start " )
( and ( is-downcase? loc ) ( not small-caves ) ) )
( set-subtract links links-with-loc )
links ) )
( for*/list ( [ link links-with-loc ]
[ next-loc ( in-value ( set-first ( set-remove link loc ) ) ) ]
[ path ( paths-from next-loc remaining-links next-lc-visited ) ] )
( cons loc path ) ) ] ) )
( check-equal? ( length ( paths-from " start " links #f ) ) 5576 )
( check-equal? ( length ( paths-from " start " links ) ) 152837 )