1 files changed, 22 insertions(+), 39 deletions(-)

M day05.lisp

@@ 14,40 14,23 @@
                 (mapcar #'parse-integer (split "," s)))
               (split " -> " line)))))
 
-;; Brute-force all combinations, time typing was cheaper than time thinking
-;; about a more elegant way to do this.
-(defun walk-line (function line count-diagonals)
+(defun walk-line (function line)
   (destructuring-bind (x1 y1 x2 y2) line
-    (cond
-      ((and (= x1 x2) (<= y1 y2))
-       (loop :for y :from y1 :to y2
-             :do (funcall function x1 y)))
-      ((= x1 x2)
-       (loop :for y :from y1 :downto y2
-             :do (funcall function x1 y)))
-      ((and (= y1 y2) (<= x1 x2))
-       (loop :for x :from x1 :to x2
-             :do (funcall function x y1)))
-      ((= y1 y2)
-       (loop :for x :from x1 :downto x2
-             :do (funcall function x y1)))
-      (count-diagonals) ;; skip diagonals here
-      ((and (<= x1 x2) (<= y1 y2))
-       (loop :for x :from x1 :to x2
-             :for y :from y1 :to y2
-             :do (funcall function x y)))
-      ((and (<= x1 x2))
-       (loop :for x :from x1 :to x2
-             :for y :from y1 :downto y2
-             :do (funcall function x y)))
-      ((and (<= y1 y2))
-       (loop :for x :from x1 :downto x2
-             :for y :from y1 :to y2
-             :do (funcall function x y)))
-      (t
-       (loop :for x :from x1 :downto x2
-             :for y :from y1 :downto y2
-             :do (funcall function x y))))))
+    (loop :with dx := (signum (- x2 x1))
+          :with dy := (signum (- y2 y1))
+
+          :for x := x1 :then (+ x dx)
+          :for y := y1 :then (+ y dy)
+
+          :do (funcall function x y)
+          :until (and (= x x2) (= y y2)))))
+
+(defmacro do-line ((x y) line &body body)
+  `(walk-line (lambda (,x ,y) ,@body) ,line))
+
+(defun is-orthographic (line)
+  (destructuring-bind (x1 y1 x2 y2) line
+    (or (= x1 x2) (= y1 y2))))
 
 (defun max-dimensions ()
   (loop :for (x1 y1 x2 y2) :in +input+


@@ 55,20 38,20 @@
         :maximize (max y1 y2) :into y
         :finally (return (list (1+ x) (1+ y)))))
 
-(defun solve (count-diags)
+(defun solve (count-diagonals)
   (loop :with (w h) := (max-dimensions)
         :with grid := (make-array (list h w) :element-type 'integer)
         :for line :in +input+
-        :do (walk-line (lambda (x y)
-                         (incf (aref grid y x)))
-                       line count-diags)
+        :when (or (is-orthographic line) count-diagonals)
+          :do (do-line (x y) line
+                (incf (aref grid y x)))
         :finally (return
                    (loop :for x :below w
                          :sum (loop :for y :below h
                                     :count (> (aref grid y x) 1))))))
 
 (defun solve-part-1 ()
-  (solve t))
+  (solve nil))
 
 (defun solve-part-2 ()
-  (solve nil))
+  (solve t))