day 24: u___u

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xenia 2020-12-24 00:29:33 -05:00
parent 1d540c780d
commit ad7e76345c
1 changed files with 80 additions and 0 deletions

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24.rkt Normal file
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#lang curly-fn racket
(require "scripts/aoc.rkt")
;; solution for day 24
; (define d->r degrees->radians)
; (define (i->e x) (inexact->exact (round x)))
(struct hex [x y z] #:transparent)
(define (hex+ a b)
(hex (+ (hex-x a) (hex-x b))
(+ (hex-y a) (hex-y b))
(+ (hex-z a) (hex-z b))))
(define *dirs* (hash
'e (hex 1 -1 0)
'ne (hex 1 0 -1)
'nw (hex 0 1 -1)
'w (hex -1 1 0)
'sw (hex -1 0 1)
'se (hex 0 -1 1)))
(define (paths->tiles input)
(define tiles (make-hash))
(for ([path (in-list input)])
(define posn
(for/fold ([posn (hex 0 0 0)]) ([p (in-list path)])
(hex+ posn (hash-ref *dirs* p))))
(hash-update! tiles posn not #f))
tiles)
(define (part1 input)
;; white is #f
;; black is #t
(define tiles (paths->tiles input))
(for/sum ([(_ v) (in-hash tiles)] #:when v) 1))
(define (part2 input)
(define tiles (paths->tiles input))
(define (step tiles)
(define new-tiles (make-hash))
(define minx (apply min (map hex-x (hash-keys tiles))))
(define maxx (apply max (map hex-x (hash-keys tiles))))
(define miny (apply min (map hex-y (hash-keys tiles))))
(define maxy (apply max (map hex-y (hash-keys tiles))))
(define minz (apply min (map hex-z (hash-keys tiles))))
(define maxz (apply max (map hex-z (hash-keys tiles))))
(for* ([x (in-range (sub1 minx) (+ maxx 2))] [y (in-range (sub1 miny) (+ maxy 2))] [z (in-range (sub1 minz) (+ maxz 2))] #:when (zero? (+ x y z)))
(define thispos (hex x y z))
(define thistile (hash-ref tiles thispos #f))
(define num-blacks (for/sum ([t (in-list (hash-values *dirs*))] #:when (hash-ref tiles (hex+ thispos t) #f)) 1))
(hash-set! new-tiles thispos
(cond
[(and thistile (or (zero? num-blacks) (> num-blacks 2))) #f]
[thistile #t]
[(= num-blacks 2) #t]
[else #f])))
new-tiles)
(define end (for/fold ([tiles tiles]) ([i (in-range 100)]) (displayln i) (step tiles)))
(for/sum ([(_ v) (in-hash end)] #:when v) 1))
;; parse input file
(define (parse fname)
(for/list ([line (in-list (file->lines fname))])
(map string->symbol (regexp-match* #px"(e|se|sw|w|nw|ne)" line))))
(module+ test
(require rackunit)
;; tests here
(displayln "no tests :("))
(module+ main
(define input (parse "inputs/24"))
(answer 24 1 (time (part1 input)))
(answer 24 2 (time (part2 input)))
(displayln "meow"))