1 files changed, 30 insertions, 32 deletions
diff --git a/AoC2023/day09/solver.lisp b/AoC2023/day09/solver.lisp
index d515317..3df0cc3 100644
--- a/AoC2023/day09/solver.lisp
+++ b/AoC2023/day09/solver.lisp
@@ -1,46 +1,44 @@
 ;;03:39
+;;04:07 Solved
+;;05:24 Painful refactorins
 (ql:quickload '(fiveam arrows transducers))
+
 (defparameter eg-input "0 3 6 9 12 15
 1 3 6 10 15 21
 10 13 16 21 30 45")
 
 (defun row-reducer (row)
-  (loop for (a b) on row by #'cdr
-        until (null b)
-        collect (- b a)))
+  (mapcar #'- (cdr row) row))
 
 (defun terminal-p (row)
-  (every #'zerop row))
+  (every #'= (cdr row) row))
 
-(defun forward (row)
+(defun get-coefs (row pick &optional acc)
   (if (terminal-p row)
-      0
-      (+  (forward (row-reducer row)) (car (last row)))))
+      (nreverse (cons (funcall pick row) acc))
+      (get-coefs (row-reducer row) pick (cons (funcall pick row) acc))))
 
-(defun backward (row)
-  (if (terminal-p row)
-      0
-      (-  (car row)  (backward (row-reducer row)))))
-
-(defun solver1 (lines)
-  (arrows:->>
-   lines
-   (mapcar (lambda (line)
-             (forward
-              (mapcar #'parse-integer (uiop:split-string line)))))
-   (apply #'+)))
-
-(defun solver2 (lines)
-  (arrows:->>
-   lines
-   (mapcar (lambda (line)
-             (backward
-              (mapcar #'parse-integer (uiop:split-string line)))))
-   (apply #'+)))
+(defun parse-line (line)
+  (mapcar #'parse-integer (uiop:split-string line)))
 
-(fiveam:test solutions
-  (fiveam:is (= 114 (solver1 (uiop:split-string eg-input :separator '(#\Newline)))))
-  (fiveam:is (= 2105961943 (solver1 (uiop:read-file-lines "input"))))
+(defun forward (line)
+  (reduce #'+ (get-coefs line (lambda (a) (car (last a))))))
 
-  (fiveam:is (= 2 (solver2 (uiop:split-string eg-input :separator '(#\Newline)))))
-  (fiveam:is (= 1019 (solver2 (uiop:read-file-lines "input")))))
+(defun backward (line)
+  (reduce #'- (get-coefs line #'car) :from-end t))
+
+(defun solver (lines key)
+  (reduce #'+
+          (mapcar #'parse-line lines)
+          :key key))
+
+(fiveam:test solutions
+  (fiveam:is (= 114 (solver (uiop:split-string eg-input :separator '(#\Newline))
+                            #'forward)))
+  (fiveam:is (= 2105961943 (solver (uiop:read-file-lines "input")
+                                   #'forward)))
+
+  (fiveam:is (= 2 (solver (uiop:split-string eg-input :separator '(#\Newline))
+                          #'backward)))
+  (fiveam:is (= 1019 (solver (uiop:read-file-lines "input")
+                             #'backward))))