1 files changed, 111 insertions, 0 deletions
diff --git a/AoC2023/day16/solver-structs.lisp b/AoC2023/day16/solver-structs.lisp
new file mode 100644
index 0000000..c28c1ca
--- /dev/null
+++ b/AoC2023/day16/solver-structs.lisp
@@ -0,0 +1,111 @@
+;;8:57
+;;10:26 part1
+;;10:53 part2
+(ql:quickload '(fiveam arrows alexandria))
+
+(defstruct ray
+  dir row col)
+
+(defun in-bounds (field ray)
+  (destructuring-bind (maxrow maxcol) (array-dimensions field)
+    (with-slots (row col) ray
+      (and (< -1 row maxrow)
+           (< -1 col maxcol)))))
+
+(defun next-direction (ray)
+  (with-slots (dir row col) ray
+    (ecase dir
+      (up (decf row))
+      (lf (decf col))
+      (dw (incf row))
+      (rt (incf col))))
+  ray)
+
+(defun mirror-bs (ray)
+  (with-slots (dir row col) ray
+    (arrows:->>
+     (ecase dir
+       (up 'lf)
+       (lf 'up)
+       (dw 'rt)
+       (rt 'dw))
+     (setf dir)))
+  ray)
+
+(defun mirror-fs (ray)
+  (with-slots (dir row col) ray
+    (arrows:->>
+     (ecase dir
+       (up 'rt)
+       (rt 'up)
+       (lf 'dw)
+       (dw 'lf))
+     (setf dir)))
+  ray)
+
+(defun split (ray alignment)
+  (with-slots (dir row col) ray
+    (mapcar (lambda (d) (make-ray :dir d :row row :col col))
+            (cond
+              ((and (eq alignment 'vertical)   (member dir '(lf rt))) '(up dw))
+              ((and (eq alignment 'horizontal) (member dir '(up dw))) '(lf rt))
+              ((list dir))))))
+
+(defun energized-p (energized ray)
+  (with-slots (dir row col) ray
+    (find dir (gethash (cons row col) energized))))
+
+(defun ensure-list (l) (if (listp l) l (list l)))
+
+(defun action (field ray energized)
+  (with-slots (dir row col) ray
+    (arrows:->>
+     (ecase (aref field row col)
+       (#\. ray)
+       (#\\ (mirror-bs ray))
+       (#\/ (mirror-fs ray))
+       (#\| (split ray 'vertical))
+       (#\- (split ray 'horizontal)))
+     (ensure-list)
+     (mapcar #'next-direction)
+     (remove-if-not (alexandria:curry #'in-bounds field))
+     (remove-if (alexandria:curry #'energized-p energized)))))
+
+(defun advancer (field rays energized)
+  (dolist (r rays)
+    (with-slots (dir row col) r
+      (push dir (gethash (cons row col) energized))))
+  (if  (null rays)
+       energized
+       (let ((next-moves (mapcan (lambda (ray) (action field ray energized)) rays)))
+         ;; (format t "~d Next: ~a~%" maxi next-moves)
+         (advancer field next-moves energized))))
+
+(defun boundary-rays (field)
+  (destructuring-bind (maxrow maxcol) (array-dimensions field)
+    (mapcar (lambda (point)
+              (destructuring-bind (dir row col) point
+                (make-ray :dir dir :row row :col col)))
+            (append
+             (loop for i below maxrow collect (list 'rt i 0))
+             (loop for i below maxrow collect (list 'lf i (1- maxcol)))
+             (loop for i below maxcol collect (list 'dw 0 i))
+             (loop for i below maxcol collect (list 'up (1- maxrow) i))))))
+
+(defun solver (field)
+  (lambda (start)
+    (hash-table-count
+     (advancer field (list start)
+               (make-hash-table :test #'equal)))))
+
+(defun solution (input &optional (starter (constantly (list (make-ray :dir 'rt :row 0 :col 0)))))
+  (let* ((rows (length input))
+         (field
+           (make-array (list rows (length (car input))) :initial-contents input)))
+    (reduce #'max (funcall starter field) :key (solver field))))
+
+(fiveam:test solutions
+  (fiveam:is (= 46 (solution (uiop:read-file-lines "eg-in"))))
+  (fiveam:is (= 7996 (solution (uiop:read-file-lines "input"))))
+  (fiveam:is (= 51 (solution (uiop:read-file-lines "eg-in") #'boundary-rays)))
+  (fiveam:is (= 8239 (solution (uiop:read-file-lines "input") #'boundary-rays))))