Flattener

README.md

Flattener

Flattener is a utility to flatten an array of arbitrarily nested arrays of integers into a flat array of integers.

Getting Started

To run the project, just create a folder and put the file flattener.js, test.js and package.json inside.

Prerequisites

• NodeJS > 6.0.0

Installing

To install

npm install

To run the code, open the node shell in the project folder (node) and run

const flattener = require("./flattener")
flattener([[1, 2, [3]], 4])

Running the tests

To run test

npm test

Regarding the tests

The tests cover multiple scenario: empty cases, undefined input, multiple nested structure.

flattener_recursive

There's a not exported recursive implementation of the flattener inside the package. This version may be more readable and shorter but can go out of memory for deeply nested arrays, so I preferred to submit the iterative version of it.

Author

• Matteo Madeddu - made2591

flattener.js

// --- Directions
// Write some code, that will flatten an array of arbitrarily
// nested arrays of integers into a flat array of integers.
// --- Examples
//   flattener([[1,2,[3]],4]) --> [1,2,3,4]

function flattener(array) {

    if (!Array.isArray(array)) throw new Error('The input value is not an array');
    var flattened = []
    if (array.length === 0) return flattened
    var stack = []
    stack.push(...array)
    while (stack.length != 0) {
        var elems = stack.shift()
        if (Array.isArray(elems)) {
            stack.unshift(...elems)
        } else {
            flattened.push(elems)
        }
    }
    return flattened;

}

// See README.md for more information
function flattener_recursive(array) {
    if (Array.isArray(array)) {
        return array.reduce(function (flattened, current) {
            return flattened.concat(flattener_recursive(current));
        }, []);
    } else {
        return array;
    }
}

module.exports = flattener;

package.json

{
  "name": "flattener",
  "version": "0.1.0",
  "description": "Flattener by made2591",
  "main": "flattener.js",
  "scripts": {
    "test": "jest"
  },
  "keywords": [
    "flattener",
    "test",
    "interview",
    "conversio",
    "excercise",
    "code"
  ],
  "author": "Matteo Madeddu <matteo.madeddu@gmail.com> (https://madeddu.xyz/)",
  "license": "MIT",
  "devDependencies": {},
  "dependencies": {
    "jest": "^24.8.0"
  }
}

test.js

const flattener = require('./flattener.js');

// function exist and it's correctly exported
test('flattener function exists', () => {
  expect(typeof flattener).toEqual('function');
});

// empty cases works
test('"[]" is the flattened form of "[]"', () => {
  expect(flattener([])).toEqual([])
});

test('"[[], [[]]]" is the flattened form of "[]"', () => {
  expect(flattener([[], [[]]])).toEqual([])
});

// easy case works
test('"[1, 2, 3]" is the flattened form of "[1, 2, 3]"', () => {
  expect(flattener([1, 2, 3])).toEqual([1, 2, 3])
});

// provided case works
test('"[1,2,3,4]" is the flattened form of "[[1,2,[3]],4]"', () => {
  expect(flattener([[1, 2, [3]], 4])).toEqual([1, 2, 3, 4])
});

// test more complex cases
test('"[[[[[[[[2, 5, 6, 4, 6]]]]]]]]" is the flattened form of "[2, 5, 6, 4, 6]"', () => {
  expect(flattener([[[[[[[[2, 5, 6, 4, 6]]]]]]]])).toEqual([2, 5, 6, 4, 6])
});

test('"[2, 5, 6, 4, 6 , 6, 3, 2, 5, 8]" is the flattened form of "[[2, 5, 6], [[4,6]], [6,3, [2, 5]], 8]"', () => {
  expect(flattener([[2, 5, 6], [[4, 6]], [6, 3, [2, 5]], 8])).toEqual([2, 5, 6, 4, 6, 6, 3, 2, 5, 8])
});

// undefined throws error
test('"undefined" input throws an error', () => {
  expect(() => { flattener(undefined) }).toThrow()
});

// string input throws error
test('string input throws an error', () => {
  expect(() => { flattener("Hello") }).toThrow()
});