From 040def513f9624329085bcb7c0ee9b60da210f9f Mon Sep 17 00:00:00 2001
From: Jonathan Chan <jcxz@cs.ubc.ca>
Date: Sat, 4 Dec 2021 22:43:10 -0800
Subject: [PATCH] Day 05: Now purely functional!

---
 src/05.rkt | 49 +++++++++++++++++++++++++++----------------------
 1 file changed, 27 insertions(+), 22 deletions(-)

diff --git a/src/05.rkt b/src/05.rkt
index d721c0f..22f7621 100644
--- a/src/05.rkt
+++ b/src/05.rkt
@@ -15,30 +15,35 @@
 (define (count-crosses grid)
   (count #{> % 1} (hash-values grid)))
 
-(define grid (make-hash))
+(define grid1
+  (for/fold ([grid (hash)])
+            ([hv hvs])
+    (match hv
+      [`(,x ,y1 ,x ,y2)
+       (for/fold ([grid grid])
+                 ([y (range (min y1 y2) (add1 (max y1 y2)))])
+         (hash-update grid `(,x ,y) add1 0))]
+      [`(,x1 ,y ,x2 ,y)
+       (for/fold ([grid grid])
+                 ([x (range (min x1 x2) (add1 (max x1 x2)))])
+         (hash-update grid `(,x ,y) add1 0))])))
 
-(for ([hv hvs])
-  (match hv
-    [`(,x ,y1 ,x ,y2)
-     (for ([y (range (min y1 y2) (add1 (max y1 y2)))])
-       (hash-update! grid `(,x ,y) add1 0))]
-    [`(,x1 ,y ,x2 ,y)
-     (for ([x (range (min x1 x2) (add1 (max x1 x2)))])
-       (hash-update! grid `(,x ,y) add1 0))]))
+(define part1 (count-crosses grid1))
 
-(define part1 (count-crosses grid))
+(define grid2
+  (for/fold ([grid grid1])
+            ([diag diags])
+    (match diag
+      [`(,x1 ,y1 ,x2 ,y2)
+       (define-values (x-offset x-step)
+         (if (>= x2 x1) (values add1 1) (values sub1 -1)))
+       (define-values (y-offset y-step)
+         (if (>= y2 y1) (values add1 1) (values sub1 -1)))
+       (for/fold ([grid grid])
+                 ([x (range x1 (x-offset x2) x-step)]
+                  [y (range y1 (y-offset y2) y-step)])
+         (hash-update grid `(,x ,y) add1 0))])))
 
-(for ([diag diags])
-  (match diag
-    [`(,x1 ,y1 ,x2 ,y2)
-     (define-values (x-offset x-step)
-       (if (>= x2 x1) (values add1 1) (values sub1 -1)))
-     (define-values (y-offset y-step)
-       (if (>= y2 y1) (values add1 1) (values sub1 -1)))
-     (for ([x (range x1 (x-offset x2) x-step)]
-           [y (range y1 (y-offset y2) y-step)])
-       (hash-update! grid `(,x ,y) add1 0))]))
-
-(define part2 (count-crosses grid))
+(define part2 (count-crosses grid2))
 
 (show-solution part1 part2)
\ No newline at end of file