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|
#lang racket
(require "../lib/utils.rkt")
(define lines
(call-with-input-file "input"
(λ (fp) (get-lines fp))))
(define mat (list->vector lines))
(define (char-at x y)
(string-ref (vector-ref mat y) x))
(define (set-mat! x y c)
(string-set! (vector-ref mat y) x c))
(define (move-stone x1 y1 x2 y2)
(define t (char-at x1 y1))
(set-mat! x1 y1 (char-at x2 y2))
(set-mat! x2 y2 t))
(define (find-new-pos x y)
(let loop ((new-y y))
(if (or (= new-y 0)
(not (char=? #\. (char-at x (- new-y 1)))))
new-y
(loop (- new-y 1)))))
(define height (vector-length mat))
(define width (string-length (vector-ref mat 0)))
(define (tilt)
(do ((y 0 (+ y 1)))
((>= y height) (void))
(do ((x 0 (+ x 1)))
((>= x width) (void))
(when (char=? #\O (char-at x y))
(move-stone x y x (find-new-pos x y))))))
(define (count)
(define sum 0)
(do ((y 0 (+ y 1)))
((>= y height) (void))
(do ((x 0 (+ x 1)))
((>= x width) (void))
(when (char=? #\O (char-at x y))
(set! sum (+ sum (- height y))))))
sum)
(tilt)
(count)
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