Initial commit

2018/day05/day05.ss

@@ -0,0 +1,28 @@
+(import :gerbil/gambit/ports)
+(import :std/iter)
+(import :std/srfi/13)
+
+(export main)
+
+(def (opposite? x y)
+     (= (abs (- (char->integer x) (char->integer y))) 32))
+
+(def (react-polymer polymer)
+     (foldl (lambda (x acc) (match acc
+			      ((cons y rest) (if (opposite? x y) rest (cons x acc)))
+			      (else (cons x acc))))
+	    '()
+	    polymer))
+
+(def (remove-unit unit polymer)
+     (string-delete (lambda (x) (char=? (char-downcase x) (char-downcase unit))) polymer))
+
+(def (find-minimal polymer)
+     (apply min
+	    (for/collect ((c (in-range (char->integer #\a) 26)))
+			 (length (react-polymer (string->list (remove-unit (integer->char c) polymer)))))))
+
+(def (main . args)
+  (def polymer (call-with-input-file "input.txt" read-line))
+  (displayln (length (react-polymer (string->list polymer))))
+  (displayln (find-minimal polymer)))