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#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
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