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#!/usr/bin/sbcl --script
;; START PART 2
(require :sb-posix)
;; END PART 2
(defconstant +width+ 101)
(defconstant +height+ 103)
(defparameter *chart*
(make-array (list +height+ +width+)))
(defstruct robot
(position nil :type (cons integer integer))
(velocity nil :type (cons integer integer)))
(defun main (filename)
(let ((robots (parse-robots filename)))
;; START PART 1
(loop for robot in robots
do (plot-on-chart (location-after-n-seconds 100 robot))
finally (return (* (sum-for-quadrant 0)
(sum-for-quadrant 1)
(sum-for-quadrant 2)
(sum-for-quadrant 3))))
;; END PART 1 START PART 2
(handler-case (sb-posix:mkdir "charts" #o755)
(sb-posix:syscall-error ())) ; EEXIST
(dotimes (i 10000)
(dotimes (x +width+)
(dotimes (y +height+)
(setf (aref *chart* y x) 0)))
(loop for robot in robots
do (plot-on-chart (location-after-n-seconds i robot))
finally (save-chart-to-bmp i)))
;; END PART 2
))
(defun parse-robots (filename)
(with-open-file (stream filename)
(loop for line = (read-line stream nil)
while line
for numbers = (extract-numbers-from-string line)
collect (make-robot :position (cons (aref numbers 0)
(aref numbers 1))
:velocity (cons (aref numbers 2)
(aref numbers 3))))))
(defun extract-numbers-from-string (string)
(loop with number-count = 4
with numbers = (make-array number-count)
for i from 0 below number-count
for start = (position-if #'integer-char-p string)
for end = (position-if-not #'integer-char-p string :start start)
do (setf (aref numbers i) (parse-integer (subseq string start end))
string (subseq string (or end (length string))))
finally (return numbers)))
(defun location-after-n-seconds (seconds robot)
(cons (mod (+ (car (robot-position robot))
(* seconds (car (robot-velocity robot))))
+width+)
(mod (+ (cdr (robot-position robot))
(* seconds (cdr (robot-velocity robot))))
+height+)))
(defun plot-on-chart (position)
(incf (aref *chart* (cdr position) (car position))))
;; START PART 1
(defconstant +quadrant-bounds+
(make-array '(4 4) :initial-contents
(let* ((x +width+)
(y +height+)
(x/2 (floor x 2))
(y/2 (floor y 2)))
`((0 0 ,x/2 ,y/2)
(,(1+ x/2) 0 ,x ,y/2)
(0 ,(1+ y/2) ,x/2 ,y)
(,(1+ x/2) ,(1+ y/2) ,x ,y)))))
(defun sum-for-quadrant (quadrant)
(loop with q1 = (aref +quadrant-bounds+ quadrant 0)
with q2 = (aref +quadrant-bounds+ quadrant 1)
with q3 = (aref +quadrant-bounds+ quadrant 2)
with q4 = (aref +quadrant-bounds+ quadrant 3)
for x from q1 below q3
sum (loop for y from q2 below q4
sum (aref *chart* y x))))
;; END PART 1
(defun integer-char-p (char)
(or (digit-char-p char) (char= char #\-)))
;; START PART 2
(defun save-chart-to-bmp (i)
(with-open-file (stream (format nil "charts/~4,'0d.bmp" i)
:direction :output
:if-exists :supersede
:element-type '(unsigned-byte 8))
(let* ((row-size (ceiling +width+ 8))
(padding (mod (- 4 (mod row-size 4)) 4))
(pixel-data-size (* +height+ (+ row-size padding)))
(pixel-data-offset (+ 14 12 6))
(file-size (+ pixel-data-offset pixel-data-size)))
;; Bitmap file header
(write-sequence '(#x42 #x4D) stream) ; ‘BM’
(write-uint file-size 4 stream)
(write-uint 0 4 stream) ; Reserved bytes
(write-uint pixel-data-offset 4 stream)
;; Bitmap information header (BITMAPCOREHEADER)
(write-uint 12 4 stream)
(write-uint +width+ 2 stream)
(write-uint +height+ 2 stream)
(write-uint 1 2 stream) ; Number of color panes
(write-uint 1 2 stream) ; Bits per pixel
;; Color table
(write-sequence '(#x00 #x00 #x00) stream) ; Black
(write-sequence '(#xFF #xFF #xFF) stream) ; White
;; Pixel data
(dotimes (y +height+)
(let ((row-data (make-array row-size :element-type '(unsigned-byte 8))))
(dotimes (x +width+)
(let ((bit (min (aref *chart* y x) 1)))
(multiple-value-bind (q r) (floor x 8)
(setf (aref row-data q)
(logior (aref row-data q)
(ash bit (- 7 r)))))))
(write-sequence row-data stream))
(dotimes (_ padding)
(write-byte 0 stream))))))
(defun write-uint (number size stream)
(dotimes (i size)
(write-byte (ldb (byte 8 (* 8 i)) number) stream)))
;; END PART 2
;; START PART 1
(format t "~d~%" (main "input"))
;; END PART 1 START PART 2
(main "input")
;; END PART 2
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