Add flatten-array (#358)

config.json

@@ -185,6 +185,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "flatten-array",
+        "name": "Flatten Array",
+        "uuid": "c738dc79-13ca-4a61-b25d-23fde54d588f",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "gigasecond",
         "name": "Gigasecond",

exercises/practice/flatten-array/.docs/instructions.md

@@ -0,0 +1,11 @@
+# Instructions
+
+Take a nested list and return a single flattened list with all values except nil/null.
+
+The challenge is to take an arbitrarily-deep nested list-like structure and produce a flattened structure without any nil/null values.
+
+For example:
+
+input: [1,[2,3,null,4],[null],5]
+
+output: [1,2,3,4,5]

exercises/practice/flatten-array/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "flatten-array.coffee"
+    ],
+    "test": [
+      "flatten-array.spec.coffee"
+    ],
+    "example": [
+      ".meta/example.coffee"
+    ]
+  },
+  "blurb": "Take a nested list and return a single list with all values except nil/null.",
+  "source": "Interview Question",
+  "source_url": "https://reference.wolfram.com/language/ref/Flatten.html"
+}

exercises/practice/flatten-array/.meta/example.coffee

@@ -0,0 +1,11 @@
+class FlattenArray
+  @flatten: (values) ->
+    values.filter (value) -> value != null and value != undefined
+      .reduce (flattened, value) ->
+        if Array.isArray value
+          flattened.concat FlattenArray.flatten value
+        else
+          flattened.concat value
+      , []
+
+module.exports = FlattenArray

exercises/practice/flatten-array/.meta/tests.toml

@@ -0,0 +1,43 @@
+# 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.
+
+[8c71dabd-da60-422d-a290-4a571471fb14]
+description = "empty"
+
+[d268b919-963c-442d-9f07-82b93f1b518c]
+description = "no nesting"
+
+[3f15bede-c856-479e-bb71-1684b20c6a30]
+description = "flattens a nested array"
+
+[c84440cc-bb3a-48a6-862c-94cf23f2815d]
+description = "flattens array with just integers present"
+
+[d3d99d39-6be5-44f5-a31d-6037d92ba34f]
+description = "5 level nesting"
+
+[d572bdba-c127-43ed-bdcd-6222ac83d9f7]
+description = "6 level nesting"
+
+[0705a8e5-dc86-4cec-8909-150c5e54fa9c]
+description = "null values are omitted from the final result"
+
+[c6cf26de-8ccd-4410-84bd-b9efd88fd2bc]
+description = "consecutive null values at the front of the list are omitted from the final result"
+
+[382c5242-587e-4577-b8ce-a5fb51e385a1]
+description = "consecutive null values in the middle of the list are omitted from the final result"
+
+[ef1d4790-1b1e-4939-a179-51ace0829dbd]
+description = "6 level nest list with null values"
+
+[85721643-705a-4150-93ab-7ae398e2942d]
+description = "all values in nested list are null"

exercises/practice/flatten-array/flatten-array.coffee

@@ -0,0 +1,4 @@
+class FlattenArray
+  @flatten: (values) ->
+
+module.exports = FlattenArray

exercises/practice/flatten-array/flatten-array.spec.coffee

@@ -0,0 +1,57 @@
+FlattenArray = require './flatten-array'
+
+describe 'Flatten Array', ->
+  it 'empty', ->
+    values = []
+    expected = []
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'no nesting', ->
+    values = [0, 1, 2]
+    expected = [0, 1, 2]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'flattens array with just integers present', ->
+    values = [1, [2, 3, 4, 5, 6, 7], 8]
+    expected = [1, 2, 3, 4, 5, 6, 7, 8]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it '5 level nesting', ->
+    values = [0, 2, [[2, 3], 8, 100, 4, [[[50]]]], -2]
+    expected = [0, 2, 2, 3, 8, 100, 4, 50, -2]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it '6 level nesting', ->
+    values = [1, [2, [[[3]]], [[4, [[[5]]]], 6, 7], 8]]
+    expected = [1, 2, 3, 4, 5, 6, 7, 8]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'null values are omitted from the final result', ->
+    values = [1, 2, null]
+    expected = [1, 2]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'consecutive null values at the front of the list are omitted from the final result', ->
+    values = [null, null, 3]
+    expected = [3]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'consecutive null values in the middle of the list are omitted from the final result', ->
+    values = [1, null, null, 4]
+    expected = [1, 4]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it '6 level nest list with null values', ->
+    values = [0, 2, [[2, 3], 8, [[100]], null, [[null]]], -2]
+    expected = [0, 2, 2, 3, 8, 100, -2]
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'all values in nested list are null', ->
+    values = [null, [[[null]]], null, null, [[null, null], null], null]
+    expected = []
+    expect(FlattenArray.flatten values).toEqual expected
+
+  it 'undefined values are omitted from the final result', ->
+    values = [1, 2, undefined]
+    expected = [1, 2]
+    expect(FlattenArray.flatten values).toEqual expected