aoc2020/16.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 16

(struct note [name test] #:transparent)

(define (valid? notes val)
  (ormap #{(note-test %) val} notes))

(define (part1 input)
  (match-define (list notes yours others) input)
  (for*/sum ([tick (in-list others)] [val (in-list tick)] #:unless (valid? notes val))
    val))

(define (part2 input)
  (match-define (list notes yours others) input)
  (define valid-tickets (filter #{andmap #{valid? notes %} %} others))
  (define (match? idx cand-note)
    (andmap #{valid? (list cand-note) (list-ref % idx)} valid-tickets))

  (define G (undirected-graph
              (for*/list ([idx (in-range (length yours))] [cand-note (in-list notes)]
                          #:when (match? idx cand-note))
                (list idx (note-name cand-note)))))
  (for/product ([elem (in-list (maximum-bipartite-matching G))]
                #:when (string-contains? (second elem) "departure"))
    (list-ref yours (first elem))))

(define (parse fname)
  (define sn string->number)
  (match-define (list notes-in yours-in others-in) (string-split (file->string fname) "\n\n"))
  (list (for/list ([line (in-list (string-split notes-in "\n"))])
          (match line
            [(pregexp #px"^([^:]+): (\\d+)\\-(\\d+) or (\\d+)-(\\d+)$"
                      (list _ name (app sn a) (app sn b) (app sn c) (app sn d)))
             (note name #{or (<= a % b) (<= c % d)})]))
        (map sn (string-split (second (string-split yours-in "\n")) ","))
        (for/list ([line (in-list (rest (string-split others-in "\n")))])
          (map sn (string-split line ",")))))

(module+ main
  (define input (parse "inputs/16"))
  (answer 16 1 (time (part1 input)))
  (answer 16 2 (time (part2 input)))
  (displayln "meow"))