advent-of-code-2024

commit 1fa917d31e78f7342ab690a3447ef3ac47c9fcd9
parent eba1e3d671fb248cdf9966ced55805a490815e97
Author: Lukas Henkel <lh@entf.net>
Date:   Thu,  5 Dec 2024 07:06:24 +0100

Simplify

Diffstat:
M
src/day-5.lisp
 | 
37
+++++++++++--------------------------

1 file changed, 11 insertions(+), 26 deletions(-)
diff --git a/src/day-5.lisp b/src/day-5.lisp
@@ -8,31 +8,18 @@
           (uiop:split-string line :separator '(#\|))))
 
 (defun parse-update (line)
-  (map 'vector
-       #'parse-integer
-       (uiop:split-string line :separator '(#\,))))
-
-(defun update-ordered-p (update rules)
-  (loop for (first second) in rules
-        for pos-first = (position first update)
-        for pos-second = (position second update)
-        unless (or
-                (null pos-first)
-                (null pos-second)
-                (< pos-first pos-second))
-          do (return nil)
-        finally (return t)))
+  (mapcar #'parse-integer
+          (uiop:split-string line :separator '(#\,))))
 
 (defun order-update (update rule-map)
   (sort update (lambda (first second)
                  (not (gethash (list second first) rule-map)))))
 
 (defun middle-page-number (update)
-  (aref update (floor (length update) 2)))
+  (nth (floor (length update) 2) update))
 
 (defun day-5 (input)
-  (loop with rules = nil
-        with rule-map = (make-hash-table :test #'equal)
+  (loop with rule-map = (make-hash-table :test #'equal)
         with processing-updates = nil
         with task-1 = 0
         with task-2 = 0
@@ -40,15 +27,13 @@
         until (null line)
         do (cond
              (processing-updates
-              (let ((update (parse-update line)))
-                (if (update-ordered-p update rules)
-                    (incf task-1 (middle-page-number update))
-                    (progn
-                      (setf update (order-update update rule-map))
-                      (incf task-2 (middle-page-number update))))))
+              (let* ((update (parse-update line))
+                     (sorted (order-update (copy-seq update) rule-map))
+                     (middle (middle-page-number sorted)))
+                (if (seq= update sorted)
+                    (incf task-1 middle)
+                    (incf task-2 middle))))
              ((string= line "")
               (setf processing-updates t))
-             (t (let ((rule (parse-rule line)))
-                  (setf (gethash rule rule-map) t)
-                  (push rule rules))))
+             (t (setf (gethash (parse-rule line) rule-map) t)))
         finally (return (values task-1 task-2))))