day13

2016/day13/input.rkt

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+#lang reader "lang.rkt"
+1358

2016/day13/lang.rkt

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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))))

2016/day13/test.rkt

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+#lang reader "lang.rkt"
+10