add nth-prime (#319)

config.json

@@ -291,6 +291,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "nth-prime",
+        "name": "Nth Prime",
+        "uuid": "30726f91-c0b9-47fc-8574-f1ff7e5179d3",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "pangram",
         "name": "Pangram",

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.vim"
+    ],
+    "test": [
+      "nth_prime.vader"
+    ],
+    "example": [
+      ".meta/example.vim"
+    ]
+  },
+  "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.vim

@@ -0,0 +1,36 @@
+function! Prime(number) abort
+  if a:number == 0
+    throw 'there is no zeroth prime'
+  elseif a:number == 1
+    return 2
+  endif
+
+  let l:tally = 1
+  let l:candidate = 1
+  while l:tally < a:number
+    let l:candidate += 2
+    if IsPrime(l:candidate)
+      let l:tally += 1
+    endif
+  endwhile
+
+  return l:candidate
+endfunction
+
+function! IsPrime(n) abort
+  if a:n <= 1
+    return 0
+  elseif a:n == 2
+    return 1
+  elseif a:n % 2 == 0
+    return 0
+  endif
+
+  for l:i in range(3, float2nr(sqrt(a:n)) + 1, 2)
+    if a:n % l:i == 0
+      return 0
+    endif
+  endfor
+
+  return 1
+endfunction

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.vader

@@ -0,0 +1,25 @@
+Execute (first prime):
+  let g:number = 1
+  let g:expected = 2
+  AssertEqual g:expected, Prime(g:number)
+
+Execute (second prime):
+  let g:number = 2
+  let g:expected = 3
+  AssertEqual g:expected, Prime(g:number)
+
+Execute (sixth prime):
+  let g:number = 6
+  let g:expected = 13
+  AssertEqual g:expected, Prime(g:number)
+
+Execute (big prime):
+  let g:number = 10001
+  let g:expected = 104743
+  AssertEqual g:expected, Prime(g:number)
+
+Execute (there is no zeroth prime):
+  let g:number = 0
+  let g:expected = 'there is no zeroth prime'
+  AssertThrows call Prime(g:number)
+  AssertEqual g:expected, g:vader_exception

exercises/practice/nth-prime/nth_prime.vim

@@ -0,0 +1,14 @@
+"
+" Given a number n, determine what the nth prime is.
+"
+" Example:
+"
+"   :echo Prime(6)
+"   13
+"
+"   :echo Prime(10001)
+"   104743
+"
+function! Prime(number) abort
+  " your implementation goes here
+endfunction