nit

2017/d3/main.rkt

@@ -37,11 +37,12 @@
 (define vals (make-hash))
 (define (neighbor-sum n)
   (define c (nth-coordinate n))
-  (define neighbor-offsets '(1 1+i +i -1+i -1 -1-1i -i 1-i))
   (hash-ref! vals c (λ () (if (= c 0)
                               1
-                              (for/sum ([n (in-list neighbor-offsets)])
-                                (hash-ref vals (+ c n) 0))))))
+                              (for*/sum ([h (in-list '(-1 0 1))]
+                                         [v (in-list '(-1 0 1))])
+                                        (define neighbor (+ h (* +i v)))
+                                        (hash-ref vals (+ c neighbor) 0))))))
 
 (define (larger-sum x)
   (for*/first ([n (in-naturals 1)]