freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/69f90c1329a94b37e2a2086d.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
69f90c1329a94b37e2a2086d	Challenge 294: Parentheses Combinations	28	challenge-294

--description--

Given an integer, n, return the number of valid combinations of n pairs of parentheses.

• A valid combination is a string where every opening parentheses has a corresponding closing parentheses, and no closing parentheses appears before its matching opening parentheses.

For example, given 2, there are 2 valid combinations:

(())
()()

--hints--

getCombinations(2) should return 2.

assert.equal(getCombinations(2), 2);

getCombinations(3) should return 5.

assert.equal(getCombinations(3), 5);

getCombinations(5) should return 42.

assert.equal(getCombinations(5), 42);

getCombinations(8) should return 1430.

assert.equal(getCombinations(8), 1430);

getCombinations(13) should return 742900.

assert.equal(getCombinations(13), 742900);

--seed--

--seed-contents--

function getCombinations(n) {

  return n;
}

--solutions--

function getCombinations(n) {
  let count = 0;

  function generate(open, close) {
    if (open === 0 && close === 0) {
      count++;
      return;
    }
    if (open > 0) generate(open - 1, close);
    if (close > open) generate(open, close - 1);
  }

  generate(n, n);
  return count;
}