2016
Matthew Butterick 8 years ago
parent 2139fc459d
commit e39fa81687

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#lang reader "lang.rkt"
1358

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#lang br/quicklang
;; http://adventofcode.com/2016/day/13
(require graph)
(provide read-syntax
(rename-out [mb #%module-begin]))
(define (read-syntax path port)
(strip-bindings
#`(module mod "lang.rkt"
#,(string->number (string-trim (port->string port))))))
(define-macro (mb NUM)
#'(#%module-begin
(solve 50 NUM)
(solve2 NUM)))
(define (solve dim num)
(define open? (make-open-pred num))
(define g (undirected-graph '((0 0))))
(for* ([x (in-range dim)]
[y (in-range dim)]
#:when (open? (list y x)))
(when (open? (list (add1 y) x))
(add-edge! g (list y x) (list (add1 y) x)))
(when (open? (list y (add1 x)))
(add-edge! g (list y x) (list y (add1 x)))))
(define path (fewest-vertices-path g '(1 1) '(31 39)))
(displayln (and path (sub1 (length path)))))
(define (solve2 num)
(define open? (make-open-pred num))
(define (nonnegative? pt) (and (not (negative? (car pt)))
(not (negative? (cadr pt)))
pt))
(let loop ([all-visited-pts empty]
[last-visited-pts '((1 1))]
[step 0])
(cond
[(= step 50)
(length (remove-duplicates (append all-visited-pts last-visited-pts)))]
[else
(loop (append last-visited-pts all-visited-pts)
(append*
(for/list ([lvp (in-list last-visited-pts)])
(match-define (list x y) lvp)
(for/list ([pt (in-list (list (list (add1 x) y)
(list x (add1 y))
(list (sub1 x) y)
(list x (sub1 y))))]
#:when (and (nonnegative? pt)
(open? pt)
(not (member pt all-visited-pts))))
pt)))
(add1 step))])))
(define (make-open-pred num)
(λ(pt)
(match-define (list x y) pt)
(define sum
(+ (* x x) (* 3 x) (* 2 x y) y (* y y) num))
(even?
(for/sum ([c (in-string (format "~b" sum))]
#:when (char=? #\1 c))
1))))

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#lang reader "lang.rkt"
10