Initial commit

2019/day24/day24.rkt

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+#lang racket
+
+(module+ test
+  (require rackunit))
+
+(define (read-input filename)
+  (for/set ([line (file->lines filename)]
+            [i (in-naturals)]
+            #:when #t
+            [c (in-string line)]
+            [j (in-naturals)]
+            #:when (eq? c #\#))
+    (make-rectangular j i)))
+
+(define (grid-size grid)
+  (define indices (flatten (map (λ (x) (list (real-part x) (imag-part x))) (set->list grid))))
+  (add1 (apply max indices)))
+
+(define (display-grid grid)
+  (define size (grid-size grid))
+  (for ([j (in-range size)])
+    (for ([i (in-range size)])
+      (if (set-member? grid (make-rectangular i j))
+          (printf "#")
+          (printf ".")))
+    (printf "~n")))
+
+(define (count-neighbours grid pos)
+  (for/sum ([step '(-i -1 +i 1)]
+            #:when (set-member? grid (+ pos step)))
+    1))
+
+(define (lives? grid pos)
+  (define n (count-neighbours grid pos))
+  (define alive (set-member? grid pos))
+  (cond
+    [(and alive (not (= 1 n))) #f]
+    [(and (not alive) (or (= 1 n) (= 2 n))) #t]
+    [else alive]))
+
+(define (step grid)
+  (define size (grid-size grid))
+  (for*/set ([i (in-range size)]
+             [j (in-range size)]
+             #:when (lives? grid (make-rectangular i j)))
+    (make-rectangular i j)))
+
+(define (biodiversity-rating grid)
+  (define size (grid-size grid))
+  (for*/sum ([i (in-range size)]
+             [j (in-range size)]
+             #:when (set-member? grid (make-rectangular i j)))
+    (expt 2 (+ i (* j size)))))
+
+(define (part1 filename)
+  (define grid (read-input filename))
+  (define final
+    (car (for/fold ([grids (list grid)])
+                   ([i (in-naturals)]
+                    #:break (member (car grids) (cdr grids)))
+           (cons (step (car grids)) grids))))
+  (biodiversity-rating final))
+
+(module+ test
+  (check-equal? (part1 "test") 2129920)
+  (check-equal? (part1 "input") 32573535))

2019/day24/input

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+..#.#
+#.##.
+.#..#
+#....
+....#

2019/day24/test

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+....#
+#..#.
+#..##
+..#..
+#....