43 lines
1.2 KiB
Racket
43 lines
1.2 KiB
Racket
#lang curly-fn racket
|
|
|
|
(require "scripts/aoc.rkt")
|
|
(require math/number-theory)
|
|
|
|
;; solution for day 13
|
|
|
|
(define (part1 input)
|
|
(match-define (cons time buses) input)
|
|
(define (find-bus x)
|
|
(for/first ([bus (in-list buses)] #:unless (equal? 'x bus) #:when (zero? (modulo x bus)))
|
|
bus))
|
|
(for*/first ([x (in-range time +inf.0)] [bus (in-value (find-bus x))] #:when bus)
|
|
(* bus (- x time))))
|
|
|
|
(define (part2 input)
|
|
(match-define (cons _ buses) input)
|
|
(define eqns
|
|
(for/fold ([eqns '()]) ([bus (in-list buses)] [i (in-naturals)] #:unless (equal? bus 'x))
|
|
(cons (cons (- bus i) bus) eqns)))
|
|
(solve-chinese (map car eqns) (map cdr eqns)))
|
|
|
|
;; parse input file
|
|
(define (parse fname)
|
|
(define input (file->lines fname))
|
|
(define time (string->number (first input)))
|
|
(define buses (for/list ([x (in-list (string-split (second input) ","))])
|
|
(match x
|
|
["x" 'x]
|
|
[_ (string->number x)])))
|
|
(cons time buses))
|
|
|
|
(module+ test
|
|
(require rackunit)
|
|
;; tests here
|
|
(displayln "no tests :("))
|
|
|
|
(module+ main
|
|
(define input (parse "inputs/13"))
|
|
(answer 13 1 (time (part1 input)))
|
|
(answer 13 2 (time (part2 input)))
|
|
(displayln "meow"))
|