Add difference-of-squares exercise (closes #27)

config.json

@@ -12,7 +12,8 @@
      "hamming",
      "word-count",
      "bob",
-     "run-length-encoding"
+     "run-length-encoding",
+     "difference-of-squares"
   ],
   "deprecated": [
 

elm-package.json

@@ -12,7 +12,8 @@
         "./exercises/hamming",
         "./exercises/word-count",
         "./exercises/bob",
-        "./exercises/run-length-encoding"
+        "./exercises/run-length-encoding",
+        "./exercises/difference-of-squares"
     ],
     "exposed-modules": [],
     "dependencies": {

exercises/difference-of-squares/DifferenceOfSquares.elm

@@ -0,0 +1 @@
+module DifferenceOfSquares (..) where

exercises/difference-of-squares/DifferenceOfSquares.example

@@ -0,0 +1,19 @@
+module DifferenceOfSquares (..) where
+
+
+squareOfSum : Int -> Int
+squareOfSum n =
+  let
+    sum = n * (n + 1) // 2
+  in
+    sum * sum
+
+
+sumOfSquares : Int -> Int
+sumOfSquares n =
+  List.sum (List.map (\m -> m * m) [0..n])
+
+
+difference : Int -> Int
+difference n =
+  squareOfSum n - sumOfSquares n

exercises/difference-of-squares/DifferenceOfSquaresTests.elm

@@ -0,0 +1,37 @@
+module Main (..) where
+
+import Task
+import Console
+import ElmTest exposing (..)
+import DifferenceOfSquares exposing (squareOfSum, sumOfSquares, difference)
+
+
+tests : Test
+tests =
+  suite
+    "DifferenceOfSquares"
+    [ suite
+        "square the sum of the numbers up to the given number"
+        [ test "square of sum 5" (assertEqual 225 (squareOfSum 5))
+        , test "square of sum 10" (assertEqual 3025 (squareOfSum 10))
+        , test "square of sum 100" (assertEqual 25502500 (squareOfSum 100))
+        ]
+    , suite
+        "sum the squares of the numbers up to the given number"
+        [ test "sum of squares 5" (assertEqual 55 (sumOfSquares 5))
+        , test "sum of squares 10" (assertEqual 385 (sumOfSquares 10))
+        , test "sum of squares 100" (assertEqual 338350 (sumOfSquares 100))
+        ]
+    , suite
+        "subtract sum of squares from square of sums"
+        [ test "difference of squares 0" (assertEqual 0 (difference 0))
+        , test "difference of squares 5" (assertEqual 170 (difference 5))
+        , test "difference of squares 10" (assertEqual 2640 (difference 10))
+        , test "difference of squares 100" (assertEqual 25164150 (difference 100))
+        ]
+    ]
+
+
+port runner : Signal (Task.Task x ())
+port runner =
+  Console.run (consoleRunner tests)

exercises/difference-of-squares/elm-package.json

@@ -0,0 +1,16 @@
+{
+    "version": "1.0.0",
+    "summary": "Exercism problems in Elm.",
+    "repository": "https://github.com/exercism/xelm.git",
+    "license": "BSD3",
+    "source-directories": [
+        "."
+    ],
+    "exposed-modules": [],
+    "dependencies": {
+        "deadfoxygrandpa/elm-test": "3.0.1 <= v < 4.0.0",
+        "elm-lang/core": "2.0.0 <= v < 4.0.0",
+        "laszlopandy/elm-console": "1.1.0 <= v < 2.0.0"
+    },
+    "elm-version": "0.15.0 <= v < 0.17.0"
+}