Add flatten-array exercise (#124)

config.json

@@ -315,6 +315,16 @@
         "difficulty": 5,
         "topics": null
       },
+      {
+        "slug": "flatten-array",
+        "name": "Flatten Array",
+        "uuid": "05847b82-2bcb-4a14-b189-db2876c511ba",
+        "practices": [],
+        "prerequisites": [
+          "vectors"
+        ],
+        "difficulty": 3
+      },
       {
         "slug": "etl",
         "name": "Etl",

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 write a function that accepts an arbitrarily-deep nested list-like structure and returns 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": [
+      "src/flatten_array.cljs"
+    ],
+    "test": [
+      "test/flatten_array_test.cljs"
+    ],
+    "example": [
+      ".meta/src/example.cljs"
+    ]
+  },
+  "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/src/example.cljs

@@ -0,0 +1,9 @@
+(ns flatten-array
+  (:refer-clojure :exclude [flatten]))
+
+(defn flatten [s]
+  (->> s
+       (tree-seq sequential? seq)
+       rest
+       (remove sequential?)
+       (remove nil?)))

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

@@ -0,0 +1,21 @@
+# This is an auto-generated file. Regular comments will be removed when this
+# file is regenerated. Regenerating will not touch any manually added keys,
+# so comments can be added in a "comment" key.
+
+[d268b919-963c-442d-9f07-82b93f1b518c]
+description = "no nesting"
+
+[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"
+
+[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/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/flatten-array/src/flatten_array.cljs

@@ -0,0 +1,5 @@
+(ns flatten-array)
+
+(defn flatten [arr] ;; <- arglist goes here
+  ;; your code goes here
+)

exercises/practice/flatten-array/test/flatten_array_test.cljs

@@ -0,0 +1,28 @@
+(ns flatten-array-test
+  (:require [clojure.test :refer [deftest is testing]]
+            [flatten-array]))
+
+(deftest flattens-array-of-ints
+  (testing "flattens array with just integers present"
+    (is (= [1 2 3 4 5 6 7 8]
+           (flatten-array/flatten [1 [2 3 4 5 6 7] 8])))))
+
+(deftest five-level-nesting
+  (testing "5 level nested list"
+    (is (= [0 2 2 3 8 100 4 50 -2]
+           (flatten-array/flatten [0 2 [[2 3] 8 100 4 [[[50]]]] -2])))))
+
+(deftest six-level-nesting
+  (testing "6 level nested list"
+    (is (= [1 2 3 4 5 6 7 8]
+           (flatten-array/flatten [1 [2 [[3]] [4 [[5]]] 6 7] 8])))))
+
+(deftest six-level-nested-with-nils
+  (testing "6 level nested list with nil values"
+    (is (= [0 2 2 3 8 100 -2]
+           (flatten-array/flatten [0 2 [[2 3] 8 [[100]] nil [[nil]]] -2])))))
+
+(deftest all-nils-list
+  (testing "All values in nested list are nil"
+    (is (empty?
+         (flatten-array/flatten [nil [[[nil]]] nil nil [[nil nil] nil] nil])))))