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day 24: use complex numbers for great faste

This commit is contained in:
xenia 2020-12-24 01:32:21 -05:00
parent b80c8d7b6b
commit c0c11034af
1 changed files with 13 additions and 28 deletions
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41
24.rkt
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@ -4,16 +4,8 @@
;; solution for day 24 ;; solution for day 24
;; constraint: x+y+z = 0 (define *dirs* (hash 'e 1-1i 'ne 1 'nw +1i 'w -1+1i 'sw -1 'se -1i))
;; this could be formalized with a contract but part2 is already slow enough tbh (define *dirs-values* (hash-values *dirs*))
(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 (paths->tiles input)
;; white is #f ;; white is #f
@ -21,8 +13,8 @@
(define tiles (make-hash)) (define tiles (make-hash))
(for ([path (in-list input)]) (for ([path (in-list input)])
(define posn (define posn
(for/fold ([posn (hex 0 0 0)]) ([p (in-list path)]) (for/fold ([posn 0]) ([p (in-list path)])
(hex+ posn (hash-ref *dirs* p)))) (+ posn (hash-ref *dirs* p))))
(hash-update! tiles posn not #f)) (hash-update! tiles posn not #f))
tiles) tiles)
@ -35,19 +27,14 @@
(define (part2 input) (define (part2 input)
(define tiles (paths->tiles input)) (define tiles (paths->tiles input))
(define neighbors-cache (make-hash))
(define (step tiles radius) (define (step tiles radius)
(define new-tiles (make-hash)) (define new-tiles (hash-copy tiles))
(for* ([x (in-range (- radius) (add1 radius))] [y (in-range (- radius) (add1 radius))] (for* ([x (in-range (- radius) (add1 radius))] [y (in-range (- radius) (add1 radius))])
[z (in-range (- radius) (add1 radius))] #:when (zero? (+ x y z))) (define thispos (make-rectangular x y))
(define thispos (hex x y z))
(define thistile (hash-ref tiles thispos #f)) (define thistile (hash-ref tiles thispos #f))
(define neighbors (hash-ref! neighbors-cache thispos
(thunk (for/list ([t (in-list (hash-values *dirs*))])
(hex+ thispos t)))))
(define num-blacks (define num-blacks
(for/sum ([neigh (in-list neighbors)] #:when (hash-ref tiles neigh #f)) 1)) (for/sum ([neigh (in-list *dirs-values*)] #:when (hash-ref tiles (+ thispos neigh) #f))
1))
(hash-set! new-tiles thispos (hash-set! new-tiles thispos
(match* (thistile num-blacks) (match* (thistile num-blacks)
[(#t (or 0 (not (or 1 2)))) #f] [(#t (or 0 (not (or 1 2)))) #f]
@ -56,13 +43,11 @@
[(#f _) #f]))) [(#f _) #f])))
new-tiles) new-tiles)
(define radius (apply max (map #{max (abs (hex-x %)) (abs (hex-y %)) (abs (hex-z %))} (define radius (apply max (map #{max (abs (real-part %)) (abs (imag-part %))}
(hash-keys tiles)))) (hash-keys tiles))))
(begin0 (count-black
(count-black (for/fold ([tiles tiles]) ([i (in-range 100)] [radius (in-range (add1 radius) +inf.0)])
(for/fold ([tiles tiles]) ([i (in-range 100)] [radius (in-range (add1 radius) +inf.0)]) (step tiles radius))))
(printf "\r\x1b[K~a/100..." i) (flush-output) (step tiles radius)))
(printf "\r\1b[Kdone\n")))
;; parse input file ;; parse input file
(define (parse fname) (define (parse fname)