Day 10

Added solutions for day10. Also added function "build-set" to utilities.lisp.

advent-of-code-2018.asd

@@ -17,4 +17,5 @@
                (:file "day6")
                (:file "day7")
                (:file "day8")
-               (:file "day9")))
+               (:file "day9")
+               (:file "day10")))

day10.lisp

@@ -0,0 +1,45 @@
+;;;; day10.lisp
+
+(in-package :advent-of-code-2018)
+
+(defun day10-parse-input ()
+  (let ((input
+          (loop-line-by-line (puzzlepath "input10.txt")
+            :collect (ppcre:register-groups-bind ((#'parse-integer x y dx dy))
+                         ("position=<( ?-?\\d+), ( ?-?\\d+)> velocity=<( ?-?\\d+), ( ?-?\\d+)>" line)
+                       (list x y dx dy)))))
+    (make-array (length input) :element-type 'list :initial-contents input)))
+
+(defun day10-step (points &optional (amount 1))
+  (loop :for point :across points
+        :do (incf (first point) (* (third point) amount))
+        :do (incf (second point) (* (fourth point) amount)))
+  points)
+
+(defun day10-boundary (points)
+  (loop :for (x y) :across points
+        :minimize x :into min-x
+        :maximize x :into max-x
+        :minimize y :into min-y
+        :maximize y :into max-y
+        :finally (return (list min-x min-y (- max-x min-x) (- max-y min-y)))))
+
+(defun day10-pretty-print (points)
+  (destructuring-bind (dx dy width height) (day10-boundary points)
+    (loop
+      :with positions := (build-set points :test 'equal :key (lambda (p) (cons (first p) (second p))))
+      :for y :upto height
+      :do (loop :for x :upto width
+                :do (format t (if (gethash (cons (+ dx x) (+ dy y)) positions) "#" " ")))
+      :do (format t "~%"))))
+
+(defun day10 ()
+  (loop :for points := (day10-parse-input) :then (day10-step points)
+        :for (nil nil width height) := (day10-boundary points)
+        :for last-area := nil :then area
+        :for area := (* width height)
+        :until (and last-area (> area last-area))
+        :count t :into seconds
+        :finally (progn
+                   (format t "After ~a seconds the following message appears:~%~%" (1- seconds))
+                   (day10-pretty-print (day10-step points -1)))))

utilities.lisp

@@ -53,3 +53,8 @@
     :for value := (aref vector index)
     :when (> value max-val) :do (setf max-ind index max-val value)
     :finally (return (values max-ind max-val))))
+
+(defun build-set (seq &key (test 'eql) (key #'identity))
+  (let ((set (make-hash-table :test test)))
+    (map nil (lambda (k) (setf (gethash (funcall key k) set) t)) seq)
+    set))