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