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