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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)
(let loop ((y 0))
(if (>= y height)
(void)
(let ()
(let loop1 ((x 0))
(if (>= x width)
(void)
(let ()
(define c (char-at x y))
(if (char=? #\O c)
(let ()
(define new-y (find-new-pos x y))
(move-stone x y x new-y)
(loop1 (+ 1 x)))
(loop1 (+ 1 x))))))
(loop (+ 1 y))))))
(define (count)
(let loop ((x 0) (y 0) (sum 0))
(if (>= y height)
sum
(if (>= x width)
(loop 0 (+ 1 y) sum)
(let ()
(define c (char-at x y))
(if (char=? c #\O)
(loop (+ 1 x) y (+ sum (- height y)))
(loop (+ 1 x) y sum)))))))
(tilt)
(count)
|
