Add nth-prime exercise (#133)

config.json

@@ -585,6 +585,18 @@
         ],
         "difficulty": 2
       },
+      {
+        "slug": "nth-prime",
+        "name": "Nth Prime",
+        "uuid": "c5121449-5340-403f-8eff-f8c46db467ff",
+        "practices": [
+          "numbers"
+        ],
+        "prerequisites": [
+          "numbers"
+        ],
+        "difficulty": 2
+      },
       {
         "slug": "robot-name",
         "name": "Robot Name",

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": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/nth_prime.cljs"
+    ],
+    "test": [
+      "test/nth_prime_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "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/src/example.cljs

@@ -0,0 +1,33 @@
+(ns nth-prime)
+
+(defn sqrt
+  "Wrapper around java's sqrt method."
+  [number]
+  (int (Math/ceil (Math/sqrt number))))
+
+(defn divides?
+  "Helper function to decide if a number is evenly divided by divisor."
+  [number divisor]
+  (zero? (mod number divisor)))
+
+(defn- prime-by-trial-division?
+  "Simple trial division prime check."
+  [number]
+  (empty? (for [n (range 3 (inc (sqrt number)) 2) :when (divides? number n)] n)))
+
+(defn prime? [number]
+  (or (= 2 number)
+      (and (odd? number) (prime-by-trial-division? number))))
+
+(defn next-prime [start]
+  (loop [n (inc start)]
+    (if (prime? n)
+      n
+      (recur (inc n)))))
+
+(def primes (iterate next-prime 1))
+
+(defn nth-prime [index]
+  (when-not (pos? index)
+    (throw (js/Error. "nth-prime expects a positive integer for an argument")))
+  (nth primes index))

exercises/practice/nth-prime/.meta/tests.toml

@@ -0,0 +1,18 @@
+# This is an auto-generated file. Regular comments will be removed when this
+# file is regenerated. Regenerating will not touch any manually added keys,
+# so comments can be added in 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/deps.edn

@@ -0,0 +1,10 @@
+{:deps
+ {org.clojure/clojure {:mvn/version "1.10.1"}
+  org.clojure/clojurescript {:mvn/version "1.10.773"}}
+
+ :aliases
+ {:test
+  {:extra-paths ["test"]
+   :extra-deps
+   {olical/cljs-test-runner {:mvn/version "3.8.0"}}
+   :main-opts ["-m" "cljs-test-runner.main"]}}}

exercises/practice/nth-prime/src/nth_prime.cljs

@@ -0,0 +1,7 @@
+(ns nth-prime)
+
+(defn nth-prime 
+  "Returns the prime number in the nth position."
+  [n] ;; <- arglist goes here
+  ;; your code goes here
+  )

exercises/practice/nth-prime/test/nth_prime_test.cljs

@@ -0,0 +1,23 @@
+(ns nth-prime-test
+  (:require [clojure.test :refer [deftest testing is]]
+            nth-prime))
+
+(deftest first-prime
+  (testing "the first prime is 2"
+    (is (= 2 (nth-prime/nth-prime 1)))))
+
+(deftest second-prime
+  (testing "the second prime is 3"
+    (is (= 3 (nth-prime/nth-prime 2)))))
+
+(deftest sixth-prime
+  (testing "the sixth prime is 13"
+    (is (= 13 (nth-prime/nth-prime 6)))))
+
+(deftest ten-thousand-first-prime
+  (testing "the ten thousand and first prime is 104743"
+    (is (= 104743 (nth-prime/nth-prime 10001)))))
+
+(deftest zeroth-prime
+  (testing "there is no zeroth prime"
+    (is (thrown? js/Error (nth-prime/nth-prime 0)))))