Add nth-prime

Author: BNAndras

config.json

@@ -230,6 +230,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "nth-prime",
+        "name": "Nth Prime",
+        "uuid": "ae46d5df-62cc-46d8-a773-bc93a1ad716e",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "nucleotide-count",
         "name": "Nucleotide Count",

exercises/practice/nth-prime/.docs/instructions.md

@@ -0,0 +1,7 @@
+# Instructions
+
+Given a number n, determine what the nth prime is.
+
+By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
+
+If your language provides methods in the standard library to deal with prime numbers, pretend they don't exist and implement them yourself.

exercises/practice/nth-prime/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "nth-prime.rkt"
+    ],
+    "test": [
+      "nth-prime-test.rkt"
+    ],
+    "example": [
+      ".meta/example.rkt"
+    ]
+  },
+  "blurb": "Given a number n, determine what the nth prime is.",
+  "source": "A variation on Problem 7 at Project Euler",
+  "source_url": "https://projecteuler.net/problem=7"
+}

exercises/practice/nth-prime/.meta/example.rkt

@@ -0,0 +1,29 @@
+#lang racket
+
+(provide nth-prime)
+
+(define/contract (nth-prime number)
+  (-> exact-positive-integer? exact-positive-integer?)
+  (let loop ([candidate 2]
+             [count 0])
+    (cond
+      [(prime? candidate)
+       (cond
+         [(= (add1 count) number) candidate]
+         [else (loop (add1 candidate)
+                     (add1 count))])]
+      [else (loop (add1 candidate)
+                  count)])))
+
+(define (prime? number)
+  (cond
+    [(zero? number) #f]
+    [(= number 1) #f]
+    [(= number 2) #t]
+    [(even? number) #f]
+    [else
+     (let loop ([factor 3])
+       (cond
+         [(> (expt factor 2) number) #t]
+         [(zero? (remainder number factor)) #f]
+         [else (loop (+ factor 2))]))]))

exercises/practice/nth-prime/.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.
+
+[75c65189-8aef-471a-81de-0a90c728160c]
+description = "first prime"
+
+[2c38804c-295f-4701-b728-56dea34fd1a0]
+description = "second prime"
+
+[56692534-781e-4e8c-b1f9-3e82c1640259]
+description = "sixth prime"
+
+[fce1e979-0edb-412d-93aa-2c744e8f50ff]
+description = "big prime"
+
+[bd0a9eae-6df7-485b-a144-80e13c7d55b2]
+description = "there is no zeroth prime"

exercises/practice/nth-prime/nth-prime-test.rkt

@@ -0,0 +1,26 @@
+#lang racket/base
+
+(require "nth-prime.rkt")
+
+(module+ test
+  (require rackunit rackunit/text-ui)
+
+  (define suite
+    (test-suite
+     "nth prime tests"
+     (test-equal? "first prime"
+                  (nth-prime 1)
+                  2)
+     (test-equal? "second prime"
+                  (nth-prime 2)
+                  3)
+     (test-equal? "sixth prime"
+                  (nth-prime 6)
+                  13)
+     (test-equal? "big prime"
+                  (nth-prime 10001)
+                  104743)
+     (test-exn "there is no zeroth prime"
+               exn:fail? (lambda () (nth-prime 0)))))
+
+  (run-tests suite))

exercises/practice/nth-prime/nth-prime.rkt

@@ -0,0 +1,6 @@
+#lang racket
+
+(provide nth-prime)
+
+(define (nth-prime number)
+  (error "Not implemented yet"))