83 lines
2.6 KiB
Racket
83 lines
2.6 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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;; constraint: x+y+z = 0
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;; this could be formalized with a contract but part2 is already slow enough tbh
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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 'e (hex 1 -1 0) 'ne (hex 1 0 -1) 'nw (hex 0 1 -1)
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'w (hex -1 1 0) 'sw (hex -1 0 1) 'se (hex 0 -1 1)))
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(define (paths->tiles input)
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;; white is #f
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;; black is #t
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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 (count-black tiles)
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(for/sum ([(_ v) (in-hash tiles)] #:when v) 1))
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(define (part1 input)
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(count-black (paths->tiles input)))
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(define (part2 input)
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(define tiles (paths->tiles input))
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(define neighbors-cache (make-hash))
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(define (step tiles radius)
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(define new-tiles (make-hash))
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(for* ([x (in-range (- radius) (add1 radius))] [y (in-range (- radius) (add1 radius))]
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[z (in-range (- radius) (add1 radius))] #: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 neighbors (hash-ref! neighbors-cache thispos
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(thunk (for/list ([t (in-list (hash-values *dirs*))])
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(hex+ thispos t)))))
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(define num-blacks
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(for/sum ([neigh (in-list neighbors)] #:when (hash-ref tiles neigh #f)) 1))
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(hash-set! new-tiles thispos
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(match* (thistile num-blacks)
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[(#t (or 0 (not (or 1 2)))) #f]
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[(#t _) #t]
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[(#f 2) #t]
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[(#f _) #f])))
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new-tiles)
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(define radius (apply max (map #{max (abs (hex-x %)) (abs (hex-y %)) (abs (hex-z %))}
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(hash-keys tiles))))
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(begin0
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(count-black
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(for/fold ([tiles tiles]) ([i (in-range 100)] [radius (in-range (add1 radius) +inf.0)])
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(printf "\r\x1b[K~a/100..." i) (flush-output) (step tiles radius)))
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(printf "\r\1b[Kdone\n")))
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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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