Data commit

Task/Dragon-curve/Racket/dragon-curve.rkt

@@ -0,0 +1,38 @@
+#lang racket
+
+(require plot)
+
+(define (dragon-turn n)
+  (if (> (bitwise-and (arithmetic-shift (bitwise-and n (- n)) 1) n) 0)
+      'L
+      'R))
+
+(define (rotate heading dir)
+  (cond
+    [(eq? dir 'R) (cond [(eq? heading 'N) 'E]
+                        [(eq? heading 'E) 'S]
+                        [(eq? heading 'S) 'W]
+                        [(eq? heading 'W) 'N])]
+    [(eq? dir 'L) (cond [(eq? heading 'N) 'W]
+                        [(eq? heading 'E) 'N]
+                        [(eq? heading 'S) 'E]
+                        [(eq? heading 'W) 'S])]))
+(define (step pos heading)
+  (cond
+    [(eq? heading 'N) (list (car pos) (add1 (cadr pos)))]
+    [(eq? heading 'E) (list (add1 (car pos)) (cadr pos))]
+    [(eq? heading 'S) (list (car pos) (sub1 (cadr pos)))]
+    [(eq? heading 'W) (list (sub1 (car pos)) (cadr pos))]
+    ))
+
+(let-values ([(dir pos trail)
+              (for/fold ([dir 'N]
+                         [pos (list 0 0)]
+                         [trail '((0 0))])
+                ([n (in-range 0 50000)])
+                (let* ([new-dir (rotate dir (dragon-turn n))]
+                       [new-pos (step pos new-dir)])
+                  (values new-dir
+                          new-pos
+                          (cons new-pos trail))))])
+  (plot-file (lines trail) "dragon.png" 'png))