Initial commit

2021/day07/day07.scm

@@ -0,0 +1,35 @@
+(import (chicken io)
+	(chicken sort)
+	srfi-1
+	srfi-152)
+
+(define (read-input #!optional (port (current-input-port)))
+  (map string->number (string-split (read-line port) ",")))
+
+(define (median lst)
+  (list-ref (sort lst <=) (/ (length lst) 2)))
+
+(define (part1 in)
+  (let ((target-pos (median in)))
+    (apply + (map (lambda (x) (abs (- x target-pos))) in))))
+
+(define (cost start end)
+  (let ((dist (abs (- start end))))
+    (/ (* dist (+ dist 1)) 2)))
+
+(define (total-fuel target-pos in)
+  (apply + (map (lambda (x) (cost target-pos x)) in)))
+
+(define (part2 in)
+  (apply min
+	 (let ((min-in (apply min in))
+	       (max-in (apply max in)))
+	   (let lp ((pos min-in)
+		    (fuels '()))
+	     (if (> pos max-in)
+		 fuels
+		 (lp (+ 1 pos) (cons (total-fuel pos in) fuels)))))))
+
+(let ((in (read-input)))
+  (print (part1 in))
+  (print (part2 in)))