Add flatten-array exercise

config.json

@@ -712,6 +712,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "flatten-array",
+        "name": "Flatten Array",
+        "uuid": "d3f7f539-dc10-4c7a-8378-7625362e8a6f",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 1
       }
     ]
   },

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": [
+    "erikschierboom"
+  ],
+  "files": {
+    "solution": [
+      "flatten-array.R"
+    ],
+    "test": [
+      "test_flatten-array.R"
+    ],
+    "example": [
+      ".meta/example.R"
+    ]
+  },
+  "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.R

@@ -0,0 +1,10 @@
+flatten <- function(input) {
+  flattened <- c()
+
+  for (element in input) {
+    if (is.null(element)) continue
+    flattened <- c(flattened, element)
+  }
+
+  flattened
+}

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.R

@@ -0,0 +1,3 @@
+flatten <- function(input) {
+
+}

exercises/practice/flatten-array/test_flatten-array.R

@@ -0,0 +1,68 @@
+source("./flatten-array.R")
+library(testthat)
+
+test_that("empty", {
+  inputs <- c()
+  expected <- c()
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("no nesting", {
+  inputs <- c(0, 1, 2)
+  expected <- c(0, 1, 2)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("flattens a nested array", {
+  inputs <- c(c(c()))
+  expected <- c()
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("flattens array with just integers present", {
+  inputs <- c(1, c(2, 3, 4, 5, 6, 7), 8)
+  expected <- c(1, 2, 3, 4, 5, 6, 7, 8)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("5 level nesting", {
+  inputs <- c(0, 2, c(c(2, 3), 8, 100, 4, c(c(c(50)))), -2)
+  expected <- c(0, 2, 2, 3, 8, 100, 4, 50, -2)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("6 level nesting", {
+  inputs <- c(1, c(2, c(c(3)), c(4, c(c(5))), 6, 7), 8)
+  expected <- c(1, 2, 3, 4, 5, 6, 7, 8)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("null values are omitted from the final result", {
+  inputs <- c(1, 2, NULL)
+  expected <- c(1, 2)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("consecutive null values at the front of the list are omitted from the final result", { # nolint
+  inputs <- c(NULL, NULL, 3)
+  expected <- c(3)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("consecutive null values in the middle of the list are omitted from the final result", { # nolint
+  inputs <- c(1, NULL, NULL, 4)
+  expected <- c(1, 4)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("6 level nest list with null values", {
+  inputs <- c(0, 2, c(c(2, 3), 8, c(c(100)), NULL, c(c(NULL))), -2)
+  expected <- c(0, 2, 2, 3, 8, 100, -2)
+  expect_equal(flatten(inputs), expected)
+})
+
+test_that("all values in nested list are null", {
+  inputs <- c(NULL, c(c(c(NULL))), NULL, NULL, c(c(NULL, NULL), NULL), NULL)
+  expected <- c()
+  expect_equal(flatten(inputs), expected)
+})