3 files changed, 48 insertions, 0 deletions
diff --git a/2024/19/.gitignore b/2024/19/.gitignore
new file mode 100644
index 0000000..5fcaefb
--- /dev/null
+++ b/2024/19/.gitignore
@@ -0,0 +1 @@
+puzzle-[12].lisp
+\ No newline at end of file
diff --git a/2024/19/Makefile b/2024/19/Makefile
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index 0000000..5a21270
--- /dev/null
+++ b/2024/19/Makefile
@@ -0,0 +1 @@
+include ../../Makefiles/lisp.mk
+\ No newline at end of file
diff --git a/2024/19/puzzles.lisp b/2024/19/puzzles.lisp
new file mode 100644
index 0000000..6d99dc8
--- /dev/null
+++ b/2024/19/puzzles.lisp
@@ -0,0 +1,46 @@
+#!/usr/bin/sbcl --script
+
+(defun main (filename)
+  (multiple-value-bind (towels stream) (parse filename)
+    (loop for pattern = (read-line stream nil)
+          while pattern
+          ;; START PART 1
+          count (plusp (nconstructions pattern towels))
+          ;; END PART 1 START PART 2
+          sum (nconstructions pattern towels)
+          ;; END PART 2
+          finally (close stream))))
+
+(defparameter *memo*
+  (let ((map (make-hash-table :test #'equal)))
+    (setf (gethash "" map) 1)
+    map))
+
+(defun nconstructions (pattern towels)
+  (multiple-value-bind (count existsp) (gethash pattern *memo*)
+    (when existsp
+      (return-from nconstructions count)))
+  (let ((count 0))
+    (dolist (towel towels)
+      (when (string-prefix-p towel pattern)
+        (incf count (nconstructions (subseq pattern (length towel)) towels))))
+    (setf (gethash pattern *memo*) count)))
+
+(defun string-prefix-p (prefix string)
+  (and (<= (length prefix) (length string))
+       (string= prefix (subseq string 0 (length prefix)))))
+
+(defun parse (filename)
+  (let* ((stream (open filename))
+         (towels (parse-strings (read-line stream))))
+    (read-line stream)                  ; Consume empty line
+    (values towels stream)))
+
+(defun parse-strings (string)
+  (loop for end = (position-if-not #'alpha-char-p string)
+        collect (subseq string 0 end) into strings
+        unless end
+          return strings
+        do (setq string (subseq string (+ 2 end)))))
+
+(format t "~d~%" (main "input"))
+\ No newline at end of file