Advent-of-Code/day15-scratch.lisp

;; https://adventofcode.com/2022/day/15
;;
;; oh, wow. i can already imagine the second part of the task
;; so. for arrangements of (sensor closest-beacon)
;; i need to figure out which points are out of rangle for all sensors?
;; where "range" is distance between sensor and the closest-beacon
;;
;; so for each sensor also store distance, and each sensor should be able to answer query for point
;; whether it disproves existence of a beacone there
;; then for ( POINTS x SENSORS ) computations i'll be able to mark all points that aren't covered.
;;
;; doesn't seem like too much

(ql:quickload 'cl-ppcre)
;; poor man's parsing
(rest (mapcar (lambda (str)
                (parse-integer str :junk-allowed t))
              (cl-ppcre:split "="
                              "Sensor at x=2, y=18: closest beacon is at x=-2, y=15")))

;; manhattan distance : https://en.wikipedia.org/wiki/Taxicab_geometry
;; sum of abs of coord-diffs

(defclass point ()
  ((x :initarg :x :reader x)
   (y :initarg :y :reader y)))

(defmethod print-object ((obj point) stream)
  (print-unreadable-object (obj stream :type t)
    (with-slots (x y)
        obj
      (format stream "x:~a y:~a" x y))))

(defparameter *test-point-1*
  (make-instance 'point :x 1 :y 19))

(defparameter *test-point-2*
  (make-instance 'point :x -2 :y -20))

(defmethod manh-dist ((one point) (two point))
  (+ (abs (- (x one) (x two)))
     (abs (- (y one) (y two)))))

(manh-dist *test-point-1* *test-point-2*)
;; i guess this is right

(defclass sensor ()
  ((self-coord :initarg :self :reader self-coord)
   (beacon-coord :initarg :beacon :reader beacon-coord)
   (covered-dist :initarg :dist :reader covered-dist)))

(defun make-sensor (sens-x sens-y beac-x beac-y)
  (let* ((sensor (make-instance 'point :x sens-x :y sens-y))
         (beacon (make-instance 'point :x beac-x :y beac-y))
         (dist (manh-dist sensor beacon)))
    (make-instance 'sensor :self sensor :beacon beacon :dist dist)))

(defmethod print-object ((obj sensor) stream)
  (print-unreadable-object (obj stream :type t)
    (with-slots (self-coord beacon-coord covered-dist)
        obj
      (format stream "at: ~a, linked to: ~a, covering dist: ~a"
              self-coord beacon-coord covered-dist))))


(defparameter *test-sensor* (make-sensor 2 18 -2 15))

(defmethod can-have-unknown-beacon-p ((p point) (s sensor))
  (> (manh-dist p (self-coord s))
      (covered-dist s)))

(manh-dist *test-point-1* (self-coord *test-sensor*))
(can-have-unknown-beacon-p *test-point-1* *test-sensor*)

(manh-dist *test-point-2* (self-coord *test-sensor*))
(can-have-unknown-beacon-p *test-point-2* *test-sensor*)

;; ok. now read in all sensors?
;; and then for line with specified 'y'
;; and from leftmost to rightmost S or B for each point ask each sensor if possible
;; to have an unknown beacon, if any says "no" - then no
;; otherwise - count

(defparameter *day15-input-file*  "day15-test.txt")


(defun line-to-coords (line)
  (rest (mapcar (lambda (str)
                  (parse-integer str :junk-allowed t))
                (cl-ppcre:split "=" line))))

(defparameter *day15-sensors-list* nil)
(setq *day15-sensors-list*
      (mapcar (lambda (coords-list)
                (apply #'make-sensor coords-list))
              (mapcar #'line-to-coords (uiop:read-file-lines *day15-input-file*))))

;; next - find lovest x and highest x
;; but then i guess i'd also want lovest and highest y overall

;; that's neat
(loop
  for sensor in *day15-sensors-list*
  minimize (x (self-coord sensor)) into xs
  minimize (x (beacon-coord sensor)) into xs
  maximize (x (self-coord sensor)) into xm
  maximize (x (beacon-coord sensor)) into xm
  minimize (y (self-coord sensor)) into ys
  minimize (y (beacon-coord sensor)) into ys
  maximize (y (self-coord sensor)) into ym
  maximize (y (beacon-coord sensor)) into ym
  finally (return (list xs xm ys ym)))
;; (-2 25 0 22)

;; now for line y=10 check all x and count how many -for-all- sensors allow new point

(defun all-sensors-allow-for-hidden-beacon (point sensors)
  (macroexpand `(and ,@(mapcar (lambda (sensor) (can-have-unknown-beacon-p point sensor))
                               sensors))))

(defun all-sensors-allow-for-hidden-beacon (point sensors)
  (not (position nil (mapcar (lambda (sensor) (can-have-unknown-beacon-p point sensor))
                             sensors))))

;; well, do i have to write my own function for AND ?
(when  (all-sensors-allow-for-hidden-beacon *test-point-2* *day15-sensors-list*)
  1)

(when  (all-sensors-allow-for-hidden-beacon *test-point-1* *day15-sensors-list*)
  1)

;; count how many ARE covered
(loop
  for x from -2 to 25
  count (not (all-sensors-allow-for-hidden-beacon
              (make-instance 'point :x x :y 10)
              *day15-sensors-list*)))

;; on the image it's from -2 and till 24, so should be 27, if counting 0
;; well. we're counting posistions "wher beacon can't possibly exist"
;; so removing points which _are_ beacons?
;;
;; and - range needs to be extended significantly, no?
;; what would be enough?
;; doubling into each direction?

(defmethod points-equal ((left point) (right point))
  (and (= (x left) (x right))
       (= (y left) (y right))))


(points-equal (make-instance 'point :x 1 :y 1)
       (make-instance 'point :x 1 :y 1))

(defun possible-to-have-beacon (point sensors)
  (let ((all-checks
          (mapcar (lambda (sensor)
                    (if (points-equal point (beacon-coord sensor))
                        'known-sensor
                        (can-have-unknown-beacon-p point sensor) ; single NIL means - not possible to have unknown
                        ))
                  sensors)))
    (or  (not (position nil all-checks)) ; nil if all sensors allow (said T) presense of unknown beacons
         (position 'known-sensor all-checks) ; exists known sensor
          )))
;; beacon is possible : either sensor has beacon at that point
;; or position is out of the sensor range
;; but here's the thing. if sencor-beacon is at this point - need to short-circuit T

(possible-to-have-beacon *test-point-2* *day15-sensors-list*)

(possible-to-have-beacon *test-point-1* *day15-sensors-list*)

(possible-to-have-beacon (make-instance 'point :x -2 :y 15) *day15-sensors-list*)

;; i guess that works

;; count how many ARE covered
(loop
  for x from -2 to 25
  count (not (possible-to-have-beacon
              (make-instance 'point :x x :y 10)
              *day15-sensors-list*)))

;; ok.