1 files changed, 61 insertions, 0 deletions
diff --git a/day08.rkt b/day08.rkt
new file mode 100644
index 0000000..25cf4ef
--- /dev/null
+++ b/day08.rkt
@@ -0,0 +1,61 @@
+#lang racket
+(require math/array)
+
+(define data (list*->array
+              (for/list ([line (file->lines "day08")])
+                (for/list ([digit (string->list line)])
+                  (- (char->integer digit) (char->integer #\0))))
+              number?))
+
+;(pretty-print data)
+
+(define visible (array->mutable-array (array-map (lambda _ 0) data)))
+
+(define height (- (vector-ref (array-shape data) 0) 1))
+(define width (- (vector-ref (array-shape data) 1) 1))
+
+(define (visit x0 dx xmax y0 dy ymax)
+  (let ((highest -1))
+    (for [(x (in-inclusive-range x0 xmax dx))
+          (y (in-inclusive-range y0 ymax dy))]
+      (let ((v (array-ref data (vector x y))))
+        (when (< highest v)
+          (set! highest v)
+          (array-set! visible (vector x y) 1))))))
+                                
+(for* [(y (in-inclusive-range 0 height))]
+  (visit 0 1 width y 0 (add1 y))
+  (visit width -1 0 y 0 (add1 y)))
+(for* [(x (in-inclusive-range 0 width))]
+  (visit x 0 (add1 x) 0 1 height)
+  (visit x 0 (add1 x) height -1 0))
+
+(array-all-sum visible)
+; 1849
+
+(define (score index)
+  (let ([h (array-ref data index)]
+        [x (vector-ref index 1)]
+        [y (vector-ref index 0)]
+        [right 0]
+        [down 0]
+        [left 0]
+        [up 0])
+    (for ([wx (in-inclusive-range (+ x 1) width 1)]
+          #:final (>= (array-ref data (vector y wx)) h))
+      (set! right (+ 1 right)))
+    (for ([wx (in-inclusive-range (- x 1) 0 -1)]
+          #:final (>= (array-ref data (vector y wx)) h))
+      (set! left (+ 1 left)))
+    (for ([wy (in-inclusive-range (+ y 1) height 1)]
+          #:final (>= (array-ref data (vector wy x)) h))
+      (set! down (+ 1 down)))
+    (for ([wy (in-inclusive-range (- y 1) 0 -1)]
+          #:final (>= (array-ref data (vector wy x)) h))
+      (set! up (+ 1 up)))
+    (* up right down left)))
+     
+(define views (array-map score (indexes-array (array-shape data))))
+
+(array-all-max views)
+; 201600