From e7e29741115ab7518d0d53f7b2c647692934cad0 Mon Sep 17 00:00:00 2001
From: Thomas Voss <mail@thomasvoss.com>
Date: Sun, 15 Dec 2024 18:14:03 +0100
Subject: Add 2024 day 15

---
 2024/15/puzzle-1.lisp | 98 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100755 2024/15/puzzle-1.lisp

(limited to '2024/15')

diff --git a/2024/15/puzzle-1.lisp b/2024/15/puzzle-1.lisp
new file mode 100755
index 0000000..16d4ac2
--- /dev/null
+++ b/2024/15/puzzle-1.lisp
@@ -0,0 +1,98 @@
+#!/usr/bin/sbcl --script
+
+(defparameter *map*       nil)
+(defparameter *moves*     nil)
+(defparameter *robot-pos* nil)
+
+(defun main (filename)
+  (parse-input filename)
+  (mapc #'handle-move *moves*)
+  (loop with (my mx) = (array-dimensions *map*)
+        for y from 0 below my
+        sum (loop for x from 0 below mx
+                  if (char= (aref *map* y x) #\O)
+                    sum (+ x (* 100 y)))))
+
+(defun handle-move (v⃗)
+  (when (can-move-p v⃗)
+    (map-setf *robot-pos* #\.)
+    (setq *robot-pos* (vec2+ *robot-pos* v⃗))
+    (when (char= #\O (aref-vec2 *map* *robot-pos*))
+      (loop for pos = *robot-pos* then (vec2+ v⃗ pos)
+            if (char= #\. (aref-vec2 *map* pos))
+              do (map-setf pos #\O)
+                 (loop-finish)))
+    (map-setf *robot-pos* #\@)))
+
+(defun can-move-p (v⃗)
+  (let ((obstacles (loop for pos = *robot-pos* then (vec2+ v⃗ pos)
+                         while (in-map-bounds-p pos)
+                         collect (aref-vec2 *map* pos))))
+    (loop for obs in obstacles
+          until (char= obs #\#)
+          if (char= obs #\.)
+            return t)))
+
+(defun in-map-bounds-p (pos)
+  (destructuring-bind (y x) (array-dimensions *map*)
+    (and (< -1 (car pos) x)
+         (< -1 (cdr pos) y))))
+
+(defun vec2+ (v⃗ u⃗)
+  (cons (+ (car v⃗) (car u⃗))
+        (+ (cdr v⃗) (cdr u⃗))))
+
+(defun aref-vec2 (array v⃗)
+  (aref array (cdr v⃗) (car v⃗)))
+
+(defun map-setf (pos val)
+  (setf (aref *map* (cdr pos) (car pos)) val))
+
+;;; Parsing
+
+(defun parse-input (filename)
+  (with-open-file (stream filename)
+    (let ((contents (make-string (file-length stream))))
+      (read-sequence contents stream)
+      (destructuring-bind (map moves)
+          (split-string contents (format nil "~%~%"))
+        (multiple-value-bind (map start-pos) (parse-map map)
+          (setq *map* map
+                *moves* (parse-moves moves)
+                *robot-pos* start-pos))))))
+
+(defun parse-map (string)
+  (let* ((first-newline (position #\Newline string))
+         (line-length (1+ first-newline))
+         (line-count (/ (1+ (length string)) line-length))
+         (map (make-array (list line-count first-newline)
+                          :element-type 'character))
+         start-pos)
+    (dotimes (y line-count)
+      (loop with start = (* y line-length)
+            for char across (subseq string start (+ start first-newline))
+            for x upfrom 0
+            if (char= char #\@)
+              do (setq start-pos (cons x y))
+            do (setf (aref map y x) char)))
+    (values map start-pos)))
+
+(defun parse-moves (string)
+  (loop for char across string
+        unless (char= char #\Newline)
+          collect (ecase char
+                    (#\^ '(0 . -1))
+                    (#\v '(0 . +1))
+                    (#\< '(-1 . 0))
+                    (#\> '(+1 . 0)))))
+
+(defun split-string (string delimiter)
+  (loop with delimiter-length = (length delimiter)
+        for end = (search delimiter string)
+        unless (eq end 0)
+          collect (subseq string 0 end) into parts
+        unless end
+          return parts
+        do (setq string (subseq string (+ end delimiter-length)))))
+
+(format t "~d~%" (main "input"))
\ No newline at end of file
-- 
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