From f8f7363dba1f63dac132702923f09954d35004c1 Mon Sep 17 00:00:00 2001
From: haskal <haskal@awoo.systems>
Date: Sat, 12 Dec 2020 00:54:22 -0500
Subject: [PATCH] day 12: rewrite using complex numbers

---
 12.rkt | 63 ++++++++++++++++++++++------------------------------------
 1 file changed, 24 insertions(+), 39 deletions(-)

diff --git a/12.rkt b/12.rkt
index dbff465..d5e05fa 100644
--- a/12.rkt
+++ b/12.rkt
@@ -6,50 +6,35 @@
 
 ;; helper functions here
 
-(define (d->r deg)
-  (* (/ deg 180) pi))
+(define d->r degrees->radians)
 
 (define (part1 input)
-  (define-values [dir x y]
-  (for/fold ([dir 0] [x 0] [y 0]) ([ins (in-list input)])
-    (match-define (cons ltr num) ins)
-    (match ltr
-      ["N" (values dir x (+ y num))]
-      ["S" (values dir x (- y num))]
-      ["E" (values dir (+ x num) y)]
-      ["W" (values dir (- x num) y)]
-      ["L" (values (+ dir (d->r num)) x y)]
-      ["R" (values (- dir (d->r num))  x y)]
-      ["F" (values dir (+ x (* num (cos dir))) (+ y (* num (sin dir))))])))
-  (inexact->exact (floor (+ (abs x) (abs y)))))
-
-(define (part2 input)
-  (define (rot x y d)
-    (values
-      (- (* x (cos d)) (* y (sin d)))
-      (+ (* x (sin d)) (* y (cos d)))))
-  (define-values [sx sy wx wy]
-    (for/fold ([sx 0] [sy 0] [wx 10] [wy 1]) ([ins (in-list input)])
+  (define-values [dir s]
+    (for/fold ([dir 0] [s 0]) ([ins (in-list input)])
       (match-define (cons ltr num) ins)
       (match ltr
-        ["N" (values sx sy wx (+ wy num))]
-        ["S" (values sx sy wx (- wy num))]
-        ["E" (values sx sy (+ wx num) wy)]
-        ["W" (values sx sy (- wx num) wy)]
-        ["L"
-         (define-values [nwx nwy] (rot wx wy (d->r num)))
-         (values sx sy nwx nwy)]
-        ["R"
-         (define-values [nwx nwy] (rot wx wy (d->r (- num))))
-         (values sx sy nwx nwy)]
-        ["F"
-         (values (+ sx (* num wx)) (+ sy (* num wy)) wx wy)])))
-  (inexact->exact (floor (+ (abs sx) (abs sy)))))
+        ["N" (values dir (+ s (* +i num)))]
+        ["S" (values dir (- s (* +i num)))]
+        ["E" (values dir (+ s num))]
+        ["W" (values dir (- s num))]
+        ["L" (values (+ dir (d->r num)) s)]
+        ["R" (values (- dir (d->r num)) s)]
+        ["F" (values dir (+ s (make-polar num dir)))])))
+  (inexact->exact (round (+ (abs (real-part s)) (abs (imag-part s))))))
 
-(module+ test
-  (require rackunit)
-  ;; tests here
-  (displayln "no tests :("))
+(define (part2 input)
+  (define-values [s w]
+    (for/fold ([s 0] [w 10+1i]) ([ins (in-list input)])
+      (match-define (cons ltr num) ins)
+      (match ltr
+        ["N" (values s (+ w (* +i num)))]
+        ["S" (values s (- w (* +i num)))]
+        ["E" (values s (+ w num))]
+        ["W" (values s (- w num))]
+        ["L" (values s (* w (make-polar 1 (d->r num))))]
+        ["R" (values s (* w (make-polar 1 (d->r (- num)))))]
+        ["F" (values (+ s (* w num)) w)])))
+  (inexact->exact (round (+ (abs (real-part s)) (abs (imag-part s))))))
 
 (module+ main
   (define input