advent-6.rkt

#lang racket
(require racket/match)

(define (get-coords sx sy ex ey)
  (for*/list ([x (in-range sx (+ 1 ex))]
              [y (in-range sy (+ 1 ey))])
    (list x y)))

(define (parse s)
  (match-let ([(list _ cmd sx sy ex ey)
               (regexp-match #rx"(turn on|turn off|toggle) ([0-9]+),([0-9]+) through ([0-9]+),([0-9]+)" s)])
    (list cmd (string->number sx) (string->number sy) (string->number ex) (string->number ey))))

(define (empty-board n)
  (list->vector (for/list ([i n]) (make-vector n #f))))

(define (update-board cmd board coords)
  (for ([c coords])
    (let* ([x (car c)]
           [y (cadr c)]
           [r (vector-ref board y)]
           [update (match cmd
                     ["turn on" (lambda (_) #t)]
                     ["turn off" (lambda (_) #f)]
                     ["toggle" (lambda (v) (not v))])])
      (vector-set! r x (update (vector-ref r x)))))
  board)

(let* ([in (open-input-file "a6.txt")]
       [lines (in-lines in)]
       [board (empty-board 1000)])

  (for ([l lines])
    (match (parse l)
      [(list cmd sx sy ex ey)
       (update-board cmd board (get-coords sx sy ex ey))]))
  (length
   (for*/list ([rs board]
               [v rs]
               #:when v)
     v)))