Initial commit

2018/day02/day02.ss

@@ -0,0 +1,39 @@
+(import :gerbil/gambit/ports)
+
+(export main)
+
+(def (unique-counts l)
+  (def hash (make-hash-table))
+  (for-each (lambda (x) (hash-update! hash x 1+ 0)) l)
+  (hash-values hash))
+
+(def (checksum l)
+  (let ((twice (length (filter (lambda (x) (memq 2 (unique-counts x))) l)))
+	(thrice (length (filter (lambda (x) (memq 3 (unique-counts x))) l))))
+    (* twice thrice)))
+
+(def (similarity id1 id2)
+  (apply +
+    (map (lambda (x y) (if (eq? x y) 0 1)) id1 id2)))
+
+(def (find-similar id id-list)
+  (filter (lambda (x) (eq? 1 (similarity id x))) id-list))
+
+(def (intersection id1 id2)
+  (reverse (foldl (lambda (x y acc) (if (eq? x y) (cons x acc) acc)) [] id1 id2)))
+
+(def (main . args)
+  (def ids (call-with-input-file "input.txt" (lambda (p) (read-all p read-line))))
+  (displayln (checksum (map string->list ids)))
+
+  (def common
+    (let/cc exit
+      (foldl
+	(lambda (id acc)
+	  (let ((similar (find-similar id acc)))
+	    (if (< 0 (length similar))
+	      (exit (intersection id (car similar)))
+	      (cons id acc))))
+	[]
+	(map string->list ids))))
+  (displayln (list->string common)))