commit 8c5d9fe59c5cb3c2439af9895b1a26a6145385ed
Author: 4903000 <4903000@chiru.no>
Date:   Wed Dec 2 13:30:38 2020 +0000

    Day 2

diff --git a/aoc20.lisp b/aoc20.lisp
new file mode 100644
index 0000000..a9873bb
--- /dev/null
+++ b/aoc20.lisp
@@ -0,0 +1,75 @@
+;;;; AoC 2020
+
+(defun read-1 (file)
+  (with-open-file (stream file)
+    (loop for line = (read-line stream nil)
+	  while line
+	  collect (parse-integer line))))
+
+(defvar *input-1-0* nil)
+(setf *input-1-0* (read-1 "inputs/1-0"))
+(defvar *input-1-1* nil)
+(setf *input-1-1* (read-1 "inputs/1-1.txt"))
+
+(defun solve-1-1 (data target)
+  (let ((deficits (map 'list (lambda (n) (- target n)) data)))
+    (reduce #'* (intersection data deficits))))
+
+(defun make-deficits (list difference)
+  (map 'list (lambda (n) (- difference n)) list))
+
+
+(defun solve-1-2 (data target)
+  (let ((first-deficits (make-deficits data target)))
+    (reduce #'*
+	    (remove-duplicates
+	     (mapcan (lambda (n)
+		       (intersection (make-deficits data n) data))
+		     first-deficits)))))
+
+(defun solve-1 (data target)
+  (time (progn
+	  (print (solve-1-1 data target))
+	  (print (solve-1-2 data target)))))
+
+(defstruct password
+  (pchar)
+  (prange)
+  (word))
+
+(defun read-2 (file)
+  (with-open-file (stream file)
+    (loop for line = (read-line stream nil)
+	  while line
+	  collect (let* ((pwlist (split-sequence:split-sequence #\space line))
+			 (range (multiple-value-bind (n index)
+				    (parse-integer (first pwlist) :junk-allowed t)
+				  (list n (parse-integer (first pwlist) :start (1+ index))))))
+		    (make-password
+		     :pchar (char (second pwlist) 0)
+		     :prange range
+		     :word (third pwlist))))))
+
+(defun %solve-2-1 (pw)
+  (let ((n (count (password-pchar pw) (password-word pw))))
+    (and (not (> (first (password-prange pw)) n))
+	 (not (< (second (password-prange pw)) n)))))
+
+(defun %solve-2-2 (pw)
+  (let ((valid 0))
+    (loop for index in (password-prange pw)
+	  do (if (eq (password-pchar pw) (elt (password-word pw) (1- index)))
+		 (incf valid)))
+    (= valid 1)))
+
+(defun %solve-2 (data test)
+  (let ((pn 0))
+    (loop for p in data
+	  do (if (funcall test p)
+		 (incf pn)))
+    pn))
+
+(defun solve-2 (file)
+  (let ((data (read-2 file)))
+    (time (progn (print (%solve-2 data #'%solve-2-1))
+		 (print (%solve-2 data #'%solve-2-2))))))