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(ql:quickload '(fiveam cl-ppcre uiop arrows))
;; Actual problem
(defun manhattan-dist (pos-sensor pos-beacon)
(destructuring-bind ((sx . sy) (bx . by)) (list pos-sensor pos-beacon)
(+ (abs (- bx sx)) (abs (- by sy)))))
(defun markers (lines)
(loop for line in lines
for (sx sy bx by) = (multiple-value-bind (match values)
(cl-ppcre:scan-to-strings "Sensor at x=(-?\\d+), y=\(-?\\d+\): closest beacon is at x=(-?\\d+), y=(-?\\d+)"
line)
(declare (ignore match))
(map 'list #'parse-integer values))
nconc (list (cons sx sy) (cons bx by))))
(defun sensor-coverage (markers)
(loop for (sensor beacon) on markers by #'cddr
collect (list sensor (manhattan-dist sensor beacon))))
(defun beacons-in-row (markers row)
(loop for (s (bx . by)) on markers by #'cddr
when (and (= row by) (not (member bx seenx)))
count by and collect bx into seenx))
(defun sensor-intervals-on-row (coverages target-row)
(sort
(loop for ((sx . sy) range) in coverages
for span = (- range (abs (- sy target-row)))
when (> span 0)
collect (list (- sx span) (+ sx span)))
#'< :key #'car))
(defun overlap-p (a b)
"Test if b=[b0;b1] overlaps a=[a0;a1]"
(destructuring-bind (a0 a1) a
(destructuring-bind (b0 b1) b
(and (<= a0 b1) (<= b0 a1)))))
(defun merge-intervals (a b)
"For overlapping interval a & b get full range"
(assert (overlap-p a b))
(destructuring-bind (a0 a1) a
(destructuring-bind (b0 b1) b
(list (min a0 b0) (max a1 b1)))))
(defun interval-accumulator (result interval)
(cond
((numberp (car result))
(list (merge-intervals result interval)))
((overlap-p (car result) interval)
(cons (merge-intervals (car result) interval)
(cdr result)))
(t (cons (car result) (cons interval (cdr result))))))
(defun interval-length (a)
(destructuring-bind (a0 a1) a
(1+ (- a1 a0))))
(defun measure-cover (markers target-row)
(arrows:-<> (sensor-coverage markers)
(sensor-intervals-on-row <> target-row)
(reduce #'interval-accumulator <>)
(reduce #'+ <> :key #'interval-length)
(- <> (beacons-in-row markers target-row))))
;; solution part 1
(fiveam:test part1
(fiveam:is (= 26 (measure-cover (markers (uiop:read-file-lines "eg-in")) 10)))
(fiveam:is (= 5040643 (measure-cover (markers (uiop:read-file-lines "input")) 2000000))))
(defun coverage-edge (sensor coverage low high test)
(destructuring-bind (x . y) sensor
(let ((edge (1+ coverage)))
(loop named dangling
for cx from (max low (- x edge)) to (min high (+ x edge))
for available = (- edge (abs (- x cx)))
:do (loop for cy in (list (- y available) (+ y available))
:when (and (<= low cy high)
(not (funcall test (cons cx cy))))
:do (return-from dangling (list cx cy)))))))
(defun point-covered (sensor-coverage)
(lambda (point)
(loop for (other-sensor range) in sensor-coverage
:thereis (<= (manhattan-dist point other-sensor) range))))
;; fail coverage too slow
(defun fail-freq (markers bound)
(loop :for y from 0 to bound
:for col = (loop :for x from 0 to bound
:when (loop :for (sensor beacon) on markers by #'cddr
:never (<= (manhattan-dist sensor (cons x y))
(manhattan-dist sensor beacon)))
:return x)
:when col
:return (+ (* 4000000 col) y)))
(defun fail-freq-edge (markers low high)
(let* ((sensor-coverage (sensor-coverage markers))
(covered-p (point-covered sensor-coverage)))
(loop for (sensor coverage) in sensor-coverage
:when (coverage-edge sensor coverage low high covered-p)
:return it)))
(defun tune-soluton (position)
(destructuring-bind (x y) position
(+ (* x 4000000) y)))
(fiveam:test part2
(fiveam:is (= 56000011 (tune-soluton (fail-freq-edge (markers (uiop:read-file-lines "eg-in")) 0 20))))
(fiveam:is (= 11016575214126 (tune-soluton (fail-freq-edge (markers (uiop:read-file-lines "input")) 2700000 3300000)))))
;; Obsolete drawing
(defun grid (bounds)
(destructuring-bind ((xmin xmax) (ymin ymax)) bounds
(make-array (* (- xmax xmin -1) (- ymax ymin -1)) :initial-element 0 :element-type '(unsigned-byte 2))))
(defun in-grid (bounds)
(destructuring-bind ((xmin xmax) (ymin ymax)) bounds
(let ((stride (- xmax xmin -1)))
(lambda (x y)
(when (and (<= xmin x xmax) (<= ymin y ymax))
(+ (- x xmin) (* (- y ymin) stride)))))))
(defun from-grid (bounds)
(destructuring-bind ((xmin xmax) (ymin _)) bounds
(declare (ignore _))
(let ((stride (- xmax xmin -1)))
(lambda (pos)
(multiple-value-bind (y x) (floor pos stride)
(cons (+ x xmin) (+ y ymin)))))))
(defun draw-grid (grid stride)
(let ((out (make-string-output-stream)))
(loop for elt across grid
for idx from 0
do (progn (when (= 0 (mod idx stride)) (terpri out))
(princ (case elt
(0 ".")
(1 "S")
(2 "B")
(3 "#")) out)))
(get-output-stream-string out)))
(defun bounds (markers)
(list (list
(loop for (x . y) in markers minimize x)
(loop for (x . y) in markers maximize x))
(list
(loop for (x . y) in markers minimize y)
(loop for (x . y) in markers maximize y))))
(defun draw-example-coverage ()
(let* ((lines (uiop:read-file-lines "eg-in"))
(markers (markers lines))
(bounds (bounds markers))
(loc (in-grid bounds))
(grid (grid bounds))
(coords (from-grid bounds)))
(loop for ((sx . sy) (bx . by)) on markers by #'cddr
do (progn (setf (aref grid (funcall loc sx sy)) 1)
(setf (aref grid (funcall loc bx by)) 2)))
(loop for (sensor beacon) on markers by #'cddr
for distance = (manhattan-dist sensor beacon)
do (loop
for elt across grid
and l from 0
when (and (<= (manhattan-dist sensor (funcall coords l)) distance) (= elt 0))
do (setf (aref grid l) 3)))
(destructuring-bind ((xmin xmax) (ymin ymax)) bounds
(declare (ignore ymax))
(let ((stride (- xmax xmin -1)))
(princ (draw-grid grid stride))
(loop repeat stride
for l from (* (+ 10 ymin) stride)
when (= 3 (aref grid l))
count it)))))
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