Complete steamroller algorithm

Author: ahcode0919

src/fcc-intermediate-algorithms/fcc-intermediate-algorithms.md

@@ -353,3 +353,15 @@ export function dropElements(arr, func) {
   return arr.slice(arr.indexOf(element));
 }
 ```
+
+#### Steamroller
+
+Flatten a nested array. You must account for varying levels of nesting.
+
+```javascript
+export function steamrollArray(arr) {
+  return arr.reduce((acc, val) => {
+    return Array.isArray(val) ? acc.concat(steamrollArray(val)) : acc.concat(val)
+  }, []);
+}
+```

src/fcc-intermediate-algorithms/steamroller.js

@@ -0,0 +1,5 @@
+export function steamrollArray(arr) {
+  return arr.reduce((acc, val) => {
+    return Array.isArray(val) ? acc.concat(steamrollArray(val)) : acc.concat(val)
+  }, []);
+}

tests/fcc-intermediate-algorithms/steamroller.test.js

@@ -0,0 +1,6 @@
+import { steamrollArray } from "../../src/fcc-intermediate-algorithms/steamroller";
+
+test('should flatten an array', () => {
+  expect(steamrollArray([[["a"]], [["b"]]])).toEqual(["a", "b"]);
+  expect(steamrollArray([1, [], [3, [[4]]]])).toEqual([1, 3, 4]);
+});