freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/basic-javascript/use-recursion-to-create-a-range-of-numbers.english.md

id, title, challengeType, forumTopicId

id	title	challengeType	forumTopicId
5cc0bd7a49b71cb96132e54c	Use Recursion to Create a Range of Numbers	1	301180

Description

Continuing from the previous challenge, we provide you another opportunity to create a recursive function to solve a problem.

Instructions

We have defined a function named rangeOfNumbers with two parameters. The function should return an array of integers which begins with a number represented by the startNum parameter and ends with a number represented by the endNum parameter. The starting number will always be less than or equal to the ending number. Your function must use recursion by calling itself and not use loops of any kind. It should also work for cases where both startNum and endNum are the same.

Tests

tests:
  - text: Your function should return an array.
    testString: assert(Array.isArray(rangeOfNumbers(5, 10)));
  - text: Your code should not use any loop syntax (<code>for</code> or <code>while</code> or higher order functions such as <code>forEach</code>, <code>map</code>, <code>filter</code>, or <code>reduce</code>).
    testString: assert(!removeJSComments(code).match(/for|while|forEach|map|filter|reduce/g));
  - text: <code>rangeOfNumbers</code> should use recursion (call itself) to solve this challenge.
    testString: assert(removeJSComments(rangeOfNumbers.toString()).match(/rangeOfNumbers\s*\(.+\)/));
  - text: <code>rangeOfNumbers(1, 5)</code> should return <code>[1, 2, 3, 4, 5]</code>.
    testString: assert.deepStrictEqual(rangeOfNumbers(1, 5), [1, 2, 3, 4, 5]);
  - text: <code>rangeOfNumbers(6, 9)</code> should return <code>[6, 7, 8, 9]</code>.
    testString: assert.deepStrictEqual(rangeOfNumbers(6, 9), [6, 7, 8, 9]);
  - text: <code>rangeOfNumbers(4, 4)</code> should return <code>[4]</code>.
    testString: assert.deepStrictEqual(rangeOfNumbers(4, 4), [4]);

Challenge Seed

function rangeOfNumbers(startNum, endNum) {
  return [];
};

After Test

const removeJSComments = str => str.replace(/\/\*[\s\S]*?\*\/|\/\/.*$/gm, '');

Solution

function rangeOfNumbers(startNum, endNum) {
  if (endNum - startNum === 0) {
    return [startNum];
  } else {
    var numbers = rangeOfNumbers(startNum, endNum - 1);
    numbers.push(endNum);
    return numbers;
  }
}