Refactor out matrix code

p81.lisp

@@ -1,27 +1,10 @@
-;;; Approach: breadth-first search, storing position and sum in a cons
-
-(defun read-matrix-from-file (path)
-  (let* ((list (mapcar (lambda (line)
-			 (mapcar #'parse-integer
-				 (uiop:split-string line :separator '(#\,))))
-		       (uiop:read-file-lines path)))
-	 (array (make-array (list (length list) (length (first list))))))
-    (loop for i upfrom 0
-	  for row in list
-	  do (loop for j upfrom 0
-		   for value in row
-		   do (setf (aref array i j) value)))
-    array))
-
+;;; Approach: lowest sum first, visiting nodes once each, storing
+;;; position and sum in a cons
 (defparameter *matrix* (read-matrix-from-file "0081_matrix.txt"))
 
 (defparameter *directions* '((1 0)
 			     (0 1)))
 
-(defun in-bounds-p (i max)
-  (and (>= i 0)
-       (< i max)))
-
 (defun path-sum-two-ways ()
   (let* ((dimensions (array-dimensions *matrix*))
 	 (goal-position (mapcar #'1- dimensions))

shared.lisp

@@ -4,6 +4,7 @@
      ,@body))
 
 (defun get-primes (max)
+  "Return a list of the first primes up to MAX"
   (let ((primes nil)
 	(composites (make-array (1+ max) :initial-element 0)))
     (loop for n from 2 upto max
@@ -12,3 +13,22 @@
 	       (loop for m from (* 2 n) upto max by n
 		     do (incf (aref composites m)))))
     (nreverse primes)))
+
+(defun read-matrix-from-file (path)
+  "Reads a two-dimensional array of integers into a matrix (2D array), from PATH"
+  (let* ((list (mapcar (lambda (line)
+			 (mapcar #'parse-integer
+				 (uiop:split-string line :separator '(#\,))))
+		       (uiop:read-file-lines path)))
+	 (array (make-array (list (length list) (length (first list))))))
+    (loop for i upfrom 0
+	  for row in list
+	  do (loop for j upfrom 0
+		   for value in row
+		   do (setf (aref array i j) value)))
+    array))
+
+(defun in-bounds-p (i max)
+  "Returns non-NIL if I is on the interval [0, MAX)"
+  (and (>= i 0)
+       (< i max)))