Add the sieve puzzle to racket

config.json

@@ -566,6 +566,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 6
+      },
+      {
+        "slug": "sieve",
+        "name": "Sieve",
+        "uuid": "1afb5b2c-1343-48cf-a17e-842b03c09981",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
       }
     ]
   },

exercises/practice/sieve/.docs/instructions.md

@@ -0,0 +1,28 @@
+# Instructions
+
+Your task is to create a program that implements the Sieve of Eratosthenes algorithm to find prime numbers.
+
+A prime number is a number that is only divisible by 1 and itself.
+For example, 2, 3, 5, 7, 11, and 13 are prime numbers.
+
+The Sieve of Eratosthenes is an ancient algorithm that works by taking a list of numbers and crossing out all the numbers that aren't prime.
+
+A number that is **not** prime is called a "composite number".
+
+To use the Sieve of Eratosthenes, you first create a list of all the numbers between 2 and your given number.
+Then you repeat the following steps:
+
+1. Find the next unmarked number in your list. This is a prime number.
+2. Mark all the multiples of that prime number as composite (not prime).
+
+You keep repeating these steps until you've gone through every number in your list.
+At the end, all the unmarked numbers are prime.
+
+~~~~exercism/note
+[Wikipedia's Sieve of Eratosthenes article][eratosthenes] has a useful graphic that explains the algorithm.
+
+The tests don't check that you've implemented the algorithm, only that you've come up with the correct list of primes.
+A good first test is to check that you do not use division or remainder operations.
+
+[eratosthenes]: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+~~~~

exercises/practice/sieve/.docs/introduction.md

@@ -0,0 +1,7 @@
+# Introduction
+
+You bought a big box of random computer parts at a garage sale.
+You've started putting the parts together to build custom computers.
+
+You want to test the performance of different combinations of parts, and decide to create your own benchmarking program to see how your computers compare.
+You choose the famous "Sieve of Eratosthenes" algorithm, an ancient algorithm, but one that should push your computers to the limits.

exercises/practice/sieve/.meta/config.json

@@ -0,0 +1,17 @@
+{
+  "authors": ["blakelewis"],
+  "files": {
+    "solution": [
+      "sieve.rkt"
+    ],
+    "test": [
+      "sieve-test.rkt"
+    ],
+    "example": [
+      ".meta/example.rkt"
+    ]
+  },
+  "blurb": "Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.",
+  "source": "Sieve of Eratosthenes at Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes"
+}

exercises/practice/sieve/.meta/example.rkt

@@ -0,0 +1,33 @@
+#lang racket
+
+(provide primes)
+
+(define (i->p i)
+  (+ (* 2 i) 3))
+
+(define (p->i p)
+  (quotient (- p 3) 2))
+
+(define (cross-out i table)
+  (let ([p (i->p i)])
+    (do
+      ([i (p->i (* p p)) (+ i p)])
+      ((>= i (vector-length table)))
+      (vector-set! table i #t))))
+
+(define (sieve limit)
+  (let* ([odds (quotient (sub1 limit) 2)]
+	 [crossed-out (make-vector odds #f)])
+    (let search ([i 0] [ps '(2)])
+      (cond [(= i odds) (reverse ps)]
+	    [(vector-ref crossed-out i) (search (add1 i) ps)]
+	    [else
+	       (begin
+		 (cross-out i crossed-out)
+		 (search (add1 i) (cons (i->p i) ps)))]))))
+
+
+(define (primes limit)
+  (if (< limit 2)
+    null
+    (sieve limit)))

exercises/practice/sieve/.meta/tests.toml

@@ -0,0 +1,25 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[88529125-c4ce-43cc-bb36-1eb4ddd7b44f]
+description = "no primes under two"
+
+[4afe9474-c705-4477-9923-840e1024cc2b]
+description = "find first prime"
+
+[974945d8-8cd9-4f00-9463-7d813c7f17b7]
+description = "find primes up to 10"
+
+[2e2417b7-3f3a-452a-8594-b9af08af6d82]
+description = "limit is prime"
+
+[92102a05-4c7c-47de-9ed0-b7d5fcd00f21]
+description = "find primes up to 1000"

exercises/practice/sieve/sieve-test.rkt

@@ -0,0 +1,39 @@
+#lang racket/base
+
+(require "sieve.rkt")
+
+(module+ test
+  (require rackunit rackunit/text-ui))
+
+(module+ test
+  (define suite
+    (test-suite
+      "sieve tests"
+
+      (test-equal? "no primes under two"
+		   (primes 1) '())
+
+      (test-equal? "find first prime"
+		   (primes 2) '(2))
+
+      (test-equal? "find primes up to 10"
+		   (primes 10) '(2 3 5 7))
+
+      (test-equal? "limit is a prime"
+		   (primes 13) '(2 3 5 7 11 13))
+
+      (test-equal? "find primes up to 1000"
+		   (primes 1000) '(
+	  2   3   5   7  11  13  17  19  23  29  31  37  41  43
+         47  53  59  61  67  71  73  79  83  89  97 101 103 107
+        109 113 127 131 137 139 149 151 157 163 167 173 179 181
+        191 193 197 199 211 223 227 229 233 239 241 251 257 263
+        269 271 277 281 283 293 307 311 313 317 331 337 347 349
+        353 359 367 373 379 383 389 397 401 409 419 421 431 433
+        439 443 449 457 461 463 467 479 487 491 499 503 509 521
+        523 541 547 557 563 569 571 577 587 593 599 601 607 613
+        617 619 631 641 643 647 653 659 661 673 677 683 691 701
+        709 719 727 733 739 743 751 757 761 769 773 787 797 809
+        811 821 823 827 829 839 853 857 859 863 877 881 883 887
+        907 911 919 929 937 941 947 953 967 971 977 983 991 997))))
+  (run-tests suite))

exercises/practice/sieve/sieve.rkt

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+#lang racket
+
+(provide primes)
+
+(define (primes limit)
+  (error "Not implemented yet"))