From 29afc863d60057ea2abb38447e69f545e294d22e Mon Sep 17 00:00:00 2001
From: 4903000 <4903000@chiru.no>
Date: Wed, 1 Dec 2021 22:24:25 +0000
Subject: [PATCH] Day 1

---
 .gitignore |  2 ++
 aoc21.lisp | 31 +++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 aoc21.lisp

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..0ab4787
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*~
+inputs/
\ No newline at end of file
diff --git a/aoc21.lisp b/aoc21.lisp
new file mode 100644
index 0000000..9c68eb5
--- /dev/null
+++ b/aoc21.lisp
@@ -0,0 +1,31 @@
+;;; Day 1
+
+(defun read-1 (file)
+  (with-open-file (stream file)
+    (loop for line = (read-line stream nil)
+	  while line
+	  collect (parse-integer line))))
+
+(defun solve-1-1 (file)
+  (let ((readings (read-1 file))
+	(inc-acc 0))
+    (labels ((rec (list old)
+	       (if list
+		   (progn
+		     (if (< old (first list))
+			 (incf inc-acc))
+		     (rec (cdr list) (first list))))))
+      (rec (cdr readings) (first readings))
+      inc-acc)))
+
+(defun solve-1-2 (file)
+  (let ((readings (read-1 file))
+	(inc-acc 0))
+    (labels ((rec (list old-sum)
+	       (if (cddr list)
+		   (let ((sum (reduce #'+ (subseq list 0 3))))
+		     (if (< old-sum sum)
+			 (incf inc-acc))
+		     (rec (cdr list) sum)))))
+      (rec (cdr readings) (reduce #'+ (subseq readings 0 3)))
+      inc-acc)))