USING: arrays assocs io.encodings.ascii io.files kernel literals
math math.extras math.functions math.parser math.vectors
pair-rocket prettyprint sequences sets splitting ;
IN: aoc2022.day09

CONSTANT: input
    $[ "vocab:aoc2022/day09/input.txt" ascii file-lines ]

CONSTANT: dirs
H{
    "U" => { -1 0 } "D" => { 1 0 }
    "L" => { 0 -1 } "R" => { 0 1 }
}

: seen  (         -- obj   ) HS{ } ;
: visit ( obj     --       ) seen adjoin ;
: tally (         -- n     ) seen cardinality ;
: near? ( u v     -- ?     ) v- [ [-1,1]? ] all? ;
: yank  ( u v     -- w     ) tuck [ - sgn ] 2map v+ ;
: tug   ( u v     -- w     ) 2dup near? [ nip ] [ yank ] if ;
: parse ( str     -- n v   ) " " split1 dec> swap dirs at ;
: pluck ( seq u   -- seq v ) swap unclip rot v+ ;
: trail ( seq u   -- v seq ) pluck tuck [ tug ] accumulate* ;
: drag  ( seq v   -- seq   ) trail swap prefix dup last visit ;
: reset (         --       ) seen clear-set ;
: line  ( seq str -- seq   ) parse '[ _ drag ] times ;
: pull  ( seq seq --       ) [ line ] each drop ;
: knots ( n       -- seq   ) { 0 0 } <array> ;
: sim   ( n       --       ) knots input pull tally . ;
: part1 (         --       ) 2 sim ;
: part2 (         --       ) 10 sim ;
: day09 (         --       ) part1 reset part2 ;

MAIN: day09