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Dimitri Lozeve 2024-11-12 21:43:32 +01:00
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(import :std/srfi/1)
(import :std/srfi/43)
(import :std/iter)
(import :gerbil/gambit/hvectors)
(export main)
(def (hundreds-digit n)
(remainder (quotient n 100) 10))
(def (power serial-number x y)
(def rack-id (+ x 10))
(- (hundreds-digit (* rack-id (+ (* rack-id y) serial-number))) 5))
(def (build-grid serial-number grid-size)
(def grid (make-vector grid-size #f))
(for ((i (in-range grid-size)))
(vector-set! grid i (make-s32vector grid-size 0)))
(for* ((i (in-range grid-size))
(j (in-range grid-size)))
(s32vector-set! (vector-ref grid i)
j
(power serial-number i j)))
(for* ((i (in-range grid-size))
(j (in-range grid-size)))
(if (> i 0)
(let ((cur-row (vector-ref grid i))
(prev-row (vector-ref grid (- i 1))))
(s32vector-set! cur-row j
(+ (s32vector-ref cur-row j)
(if (> j 0) (s32vector-ref cur-row (- j 1)) 0)
(s32vector-ref prev-row j)
(if (> j 0) (- (s32vector-ref prev-row (- j 1))) 0))))
(let ((cur-row (vector-ref grid i)))
(s32vector-set! cur-row j
(+ (s32vector-ref cur-row j)
(if (> j 0) (s32vector-ref cur-row (- j 1)) 0))))))
grid)
(def (largest-power-cell grid cell-size)
(def grid-size (vector-length grid))
(def max -10000)
(def max-idx [0 0])
(for* ((i (in-range (- grid-size cell-size)))
(j (in-range (- grid-size cell-size))))
(let* ((top-row (vector-ref grid i))
(bottom-row (vector-ref grid (+ i cell-size)))
(sum (- (+ (s32vector-ref bottom-row (+ j cell-size))
(s32vector-ref top-row j))
(+ (s32vector-ref bottom-row j)
(s32vector-ref top-row (+ j cell-size))))))
(when (> sum max)
(begin
(set! max sum)
(set! max-idx [(1+ i) (1+ j)])))))
(cons max max-idx))
(def (largest-power-cell-size grid)
(def grid-size (vector-length grid))
(def max-size 0)
(def max -1000)
(def res #f)
(for ((size (in-range grid-size)))
(let ((x (largest-power-cell grid size)))
(when (> (car x) max)
(begin
(set! max (car x))
(set! max-size size)
(set! res (cons size x))))))
res)
(def (main (serial-number "9005") . args)
(def grid (build-grid (string->number serial-number) 300))
(displayln (largest-power-cell grid 3))
(displayln (largest-power-cell-size grid)))