USING: arrays hash-sets io.encodings.utf8 io.files kernel math
math.order math.parser math.statistics math.vectors prettyprint
sequences sets splitting ;
IN: aoc.18

: input      (       -- lines  ) "~/factor/aoc/18/18.in" utf8 file-lines ;
: I          (       -- points ) input [ "," split [ dec> ] map ] map ;
: neighbours ( point -- points ) { { 1 0 0 } { -1 0 0 } { 0 1 0 } { 0 -1 0 } { 0 0 1 } { 0 0 -1 } } [ v+ ] with map ;

: count-sides ( points point -- n ) neighbours swap without length ;
: air-tiles   ( points       -- n ) [ >hash-set ] keep [ count-sides ] with map-sum ;
: part1       (              -- n ) I air-tiles ;

DEFER: flood
:: valid?          ( points minmax point -- ? ) point [ minmax first2 between? ] all? not point points in? or ;
: flood-neighbours ( points minmax point --   ) neighbours [ flood ] 2with each ;
: add-point        ( points minmax point --   ) nip swap adjoin ;
: flood            ( points minmax point --   ) 3dup valid? [ 3drop ] [ [ add-point ] 3keep flood-neighbours ] if ;

: fill-outside ( seq -- seq ) [ >hash-set dup ] keep concat [ minmax 2array ] [ infimum dup dup 3array ] bi flood members ;
: surface-area ( seq -- n   ) concat range 1 + sq 6 * ;
: part2        (     -- n   ) I fill-outside [ air-tiles ] [ surface-area ] bi - part1 swap - ;

: solve ( -- ) part1 . part2 . ;