Add grains exercise (#128)

config.json

@@ -585,6 +585,16 @@
         ],
         "difficulty": 2
       },
+      {
+        "slug": "grains",
+        "name": "Grains",
+        "uuid": "3a96556b-4ec8-431d-a5ee-99355065baec",
+        "practices": [],
+        "prerequisites": [
+          "numbers"
+        ],
+        "difficulty": 3
+      },
       {
         "slug": "proverb",
         "name": "Proverb",

exercises/practice/grains/.docs/instructions.md

@@ -0,0 +1,15 @@
+# Instructions
+
+Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
+
+There once was a wise servant who saved the life of a prince.
+The king promised to pay whatever the servant could dream up.
+Knowing that the king loved chess, the servant told the king he would like to have grains of wheat.
+One grain on the first square of a chess board, with the number of grains doubling on each successive square.
+
+There are 64 squares on a chessboard (where square 1 has one grain, square 2 has two grains, and so on).
+
+Write code that shows:
+
+- how many grains were on a given square, and
+- the total number of grains on the chessboard

exercises/practice/grains/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ErikSchierboom"
+  ],
+  "files": {
+    "solution": [
+      "src/grains.cljs"
+    ],
+    "test": [
+      "test/grains_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "blurb": "Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.",
+  "source": "The CodeRanch Cattle Drive, Assignment 6",
+  "source_url": "https://coderanch.com/wiki/718824/Grains"
+}

exercises/practice/grains/.meta/src/example.cljs

@@ -0,0 +1,16 @@
+(ns grains)
+
+(defn- pow [x n]
+  (loop [x x n n r 1]
+    (cond
+      (= n 0) r
+      (even? n) (recur (* x x) (/ n 2) r)
+      :else (recur x (dec n) (* r x)))))
+
+(defn square [number]
+  (pow 2 (dec number)))
+
+(def ^:private square-numbers (rest (range 65)))
+
+(defn total []
+  (apply + (map square square-numbers)))

exercises/practice/grains/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/grains/src/grains.cljs

@@ -0,0 +1,9 @@
+(ns grains)
+
+(defn square [] ;; <- arglist goes here
+    ;; your code goes here
+)
+
+(defn total []  ;; <- arglist goes here
+    ;; your code goes here
+)

exercises/practice/grains/test/grains_test.cljs

@@ -0,0 +1,27 @@
+(ns grains-test
+  (:require [clojure.test :refer [deftest is]]
+            grains))
+
+(deftest square-1
+  (is (= 1 (grains/square 1))))
+
+(deftest square-2
+  (is (= 2 (grains/square 2))))
+
+(deftest square-3
+  (is (= 4 (grains/square 3))))
+
+(deftest square-4
+  (is (= 8 (grains/square 4))))
+
+(deftest square-16
+  (is (= 32768 (grains/square 16))))
+
+(deftest square-32
+  (is (= 2147483648 (grains/square 32))))
+
+(deftest square-64
+  (is (= 9223372036854775808 (grains/square 64))))
+
+(deftest total-grains
+  (is (= 18446744073709551615  (grains/total))))