Data commit

Task/Cuban-primes/Racket/cuban-primes.rkt

@@ -0,0 +1,38 @@
+#lang racket
+
+(require math/number-theory
+         racket/generator)
+
+(define (make-cuban-prime-generator)
+  (generator ()
+             (let loop ((y 1) (y3 1))
+               (let* ((x (+ y 1))
+                      (x3 (expt x 3))
+                      (p (quotient (- x3 y3) (- x y))))
+                 (when (prime? p) (yield p))
+                 (loop x x3)))))
+
+(define (tabulate l (line-width 80))
+  (let* ((w (add1 (string-length (argmax string-length (map ~a l)))))
+         (cols (quotient line-width w)))
+    (for ((n (in-range 1 (add1 (length l))))
+          (i l))
+      (display (~a i #:width w #:align 'right))
+      (when (zero? (modulo n cols)) (newline)))))
+
+(define (progress-report x)
+  (when (zero? (modulo x 1000))
+    (eprintf (if (zero? (modulo x 10000)) "|" "."))
+    (flush-output (current-error-port))))
+
+(let ((200-cuban-primes (for/list ((_ 200)
+                                   (p (in-producer (make-cuban-prime-generator))))
+                          p)))
+  (tabulate 200-cuban-primes))
+
+(begin0
+  (for/last ((x 100000)
+             (p (in-producer (make-cuban-prime-generator))))
+    (progress-report x)
+    p)
+  (newline))