aoc2022/7.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 7

(define (calculate-all-sizes input)
  (define file-tree (make-hash))

  (define (ft-add-file! ft path name size)
    (match path
      ['() (hash-set! ft name size)]
      [(cons fst rst)
       (ft-add-file! (hash-ref! ft fst make-hash) rst name size)]))

  (for/fold ([cwd '()]) ([inst (in-list input)])
    (match inst
      [(list 'cd "/") '()]
      [(list 'cd "..")
       (match cwd
         ['() '()]
         [(cons _ rst) rst])]
      [(list 'cd dir) (cons dir cwd)]
      [(list 'ls) cwd]
      [(list 'dir x) cwd]
      [(list 'file file size)
       (ft-add-file! file-tree (reverse cwd) file size)
       cwd]))

  (define sizes '())

  (define (record-size! ft)
    (define size
      (for/sum ([(k v) (in-hash ft)])
        (if (number? v)
          v
          (record-size! v))))
    (set! sizes (cons size sizes))
    size)

  (record-size! file-tree)
  (sort sizes <))

(define (part1 input)
  (define *at-most* 100000)
  (apply + (filter #{< % *at-most*} (calculate-all-sizes input))))

(define (part2 input)
  (define *max-used* (- 70000000 30000000))

  (define sizes (calculate-all-sizes input))
  (define needed-to-free (- (last sizes) *max-used*))
  (findf #{>= % needed-to-free} sizes))

(define (parse fname)
  (for/list ([line (in-list (file->lines fname))])
    (match line
      [(pregexp #px"^\\$ cd (.*)$" (list _ dir))
       (list 'cd dir)]
      [(pregexp #px"^\\$ ls$")
       (list 'ls)]
      [(pregexp #px"^dir (.*)$" (list _ dir))
       (list 'dir dir)]
      [(pregexp #px"^([0-9]+) (.*)$" (list _ (app string->number size) file))
       (list 'file file size)])))

(module+ main
  (define input (parse "inputs/7"))
  (answer 7 1 (time (part1 input)))
  (answer 7 2 (time (part2 input)))
  (displayln "meow"))