freecodecamp--freecodecamp/curriculum/challenges/english/blocks/daily-coding-challenges-javascript/6a0dcd03ee4e68698080ef68.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
6a0dcd03ee4e68698080ef68	Challenge 304: Itinerary Arrangements	28	challenge-304

--description--

Given an array of at least two optional stops for a day trip, return the number of valid itinerary arrangements.

The itinerary always includes "breakfast", "lunch", and "dinner", these will not be passed in as arguments. The optional stops can be placed anywhere in the itinerary, subject to the following rules:

• "breakfast" is always first, with at least one stop before "lunch".
• "lunch" must appear before "dinner", with at least one stop in between.
• At most, one optional stop may appear after "dinner".

Return the number of valid arrangements.

--hints--

getItineraryCount(["library", "park"]) should return 2.

assert.equal(getItineraryCount(["library", "park"]), 2);

getItineraryCount(["library", "park", "arcade"]) should return 18.

assert.equal(getItineraryCount(["library", "park", "arcade"]), 18);

getItineraryCount(["library", "park", "arcade", "store"]) should return 120.

assert.equal(getItineraryCount(["library", "park", "arcade", "store"]), 120);

getItineraryCount(["library", "park", "arcade", "store", "cafe"]) should return 840.

assert.equal(getItineraryCount(["library", "park", "arcade", "store", "cafe"]), 840);

getItineraryCount(["library", "park", "arcade", "store", "cafe", "market", "museum"]) should return 55440.

assert.equal(getItineraryCount(["library", "park", "arcade", "store", "cafe", "market", "museum"]), 55440);

--seed--

--seed-contents--

function getItineraryCount(stops) {

  return stops;
}

--solutions--

function getItineraryCount(stops) {
  const items = ["lunch", "dinner", ...stops];
  let count = 0;

  function permute(arr) {
    if (arr.length === 0) return [[]];
    return arr.flatMap((item, i) =>
      permute([...arr.slice(0, i), ...arr.slice(i + 1)]).map(p => [item, ...p])
    );
  }

  for (const perm of permute(items)) {
    const lunchIdx = perm.indexOf("lunch");
    const dinnerIdx = perm.indexOf("dinner");

    if (lunchIdx >= dinnerIdx) continue;
    if (lunchIdx < 1) continue;
    if (dinnerIdx - lunchIdx < 2) continue;
    if (perm.length - dinnerIdx - 1 > 1) continue;

    count++;
  }

  return count;
}