1 files changed, 42 insertions, 58 deletions
diff --git a/report-repair/rr.scm b/report-repair/rr.scm
index b327d3c..6adee86 100644
--- a/report-repair/rr.scm
+++ b/report-repair/rr.scm
@@ -2,64 +2,48 @@
 -e main -s
 !#
 (define-module (rr)
+  #:use-module (combinations)
   #:use-module (srfi srfi-1)
+  #:use-module (ice-9 format)
   #:use-module (ice-9 exceptions)
   #:export (rr
-	    multiply-pair
-	    return-equivalent-pair
-	    equivalent-pair?
-	    return-friendship-pair
-	    report->pairs))
-
-
-(define (rr str)
-  (multiply-pair
-   (return-equivalent-pair
-    (report->pairs str))))
-
-(define (multiply-pair pair)
-  (* (car pair)
-     (cdr pair)))
-
-(define (return-equivalent-pair pairs)
-  "Given PAIRS friendship pairs, returns the
-ones that are found to be friends. Throws
-friendship-exception if no friends are found.
-
-We do NOT care if there are multiple pairs.
-Return the first one."
-  (let loop ((pair (car pairs)) (pairs (cdr pairs)))
-    (if (null? pairs)
-	(raise-exception
-	 (make-exception-with-message
-	  "Concerning lack of friendship!"))
-	(if (equivalent-pair? pair pairs)
-	    pair
-	    (loop (car pairs) (cdr pairs))))))
-
-(define (equivalent-pair? pair pairs)
-  "Given friendship pair PAIR and a list
-of other PAIRS, determines if PAIR is
-contained in PAIRS, irrespective of order"
-  (let ((r-pair (cons (cdr pair)
-		      (car pair))))
-    (any (lambda (pair)
-	   (equal? r-pair pair))
-	 pairs)))
-
-(define (report->pairs str)
-  "Given a report, convert it to a
-list of friendship pairs."
-  (let ((lst (string-split
-	      (string-trim-both str char-set:whitespace)
-	      char-set:whitespace)))
-    (map (lambda (str)
-	   (return-friendship-pair
-	    (string->number str)))
-	 lst)))
-
-(define (return-friendship-pair num)
-  "Given NUM, returns a cons pair with
-CAR as the original number and CDR as
-the companion number."
-  (cons num (- 2020 num)))
+	    get-2020-terms
+	    includes-all?
+	    generate-sets
+	    make-complete-set))
+
+(define (rr str len)
+  (apply * (get-2020-terms (map string->number
+				(string-split
+				 (string-trim-both str char-set:whitespace)
+				 char-set:whitespace))
+			   len)))
+
+(define (get-2020-terms lst len)
+  "Given a list of numbers, returns a list
+of length LEN whose contents add up to 2020.
+
+Throws input-exception if none are found."
+  (let loop ((sets (generate-sets lst len)))
+    (cond
+     ((null? sets) (raise-exception
+		    (make-exception-with-message
+		     (format #f "Could not find ~s arguments that add to 2020 in inputs!" len))))
+     ((includes-all? (car sets) lst) (car sets))
+     (#t (loop (cdr sets))))))
+
+(define (includes-all? lst1 lst2)
+  "Returns #t if all elements in LST1
+are present in LST2, #f otherwise."
+  (equal? lst1
+	  (lset-intersection eqv? lst1 lst2)))
+
+(define (generate-sets lst len)
+  (map make-complete-set (combinations lst (1- len))))
+
+(define (make-complete-set lst)
+  "Given a LST of numbers, i.e.
+'(979 366)
+returns a list of one greater length
+such that all numbers add up to 2020."
+  (append (list (- 2020 (apply + lst))) lst))