aoc2022/5.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 5

(define (solution input reverse?)
  (for/fold ([stacks (first input)] #:result (list->string (map first stacks)))
            ([move (in-list (second input))])
    (match-define (list ct (app sub1 from) (app sub1 to)) move)
    (define movement ((if reverse? reverse identity)
                      (take (list-ref stacks from) ct)))
    (list-update (list-update stacks from #{drop % ct})
                 to #{append movement %})))

(define (part1 input) (solution input #t))
(define (part2 input) (solution input #f))

(define (parse fname)
  (match-define (list stacks moves) (string-split (file->string fname) "\n\n"))
  (match-define (list stack-lines ... (app string->list cols-line)) (string-split stacks "\n"))
  (define columns (indexes-where cols-line #{not (equal? % #\space)}))
  (list
    (for/list ([col (in-list columns)])
      (for*/list ([line (in-list stack-lines)]
                  [letter (in-value (string-ref line col))]
                  #:unless (equal? #\space letter))
        letter))
    (for/list ([line (in-list (string-split moves "\n"))])
      (match-define (pregexp #px"move (\\d+) from (\\d+) to (\\d+)" (app rest move-data)) line)
      (map string->number move-data))))

(module+ main
  (define input (parse "inputs/5"))
  (answer 5 1 (time (part1 input)))
  (answer 5 2 (time (part2 input)))
  (displayln "meow"))