freeCodeCamp/curriculum/challenges/english/99-dev-playground/daily-coding-challenges-javascript/javascript-challenge-22.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
6821ebf8237de8297eaee798	JavaScript Challenge 22: Tribonacci Sequence	28	javascript-challenge-22

--description--

The Tribonacci sequence is a series of numbers where each number is the sum of the three preceding ones. When starting with 0, 0 and 1, the first 10 numbers in the sequence are 0, 0, 1, 1, 2, 4, 7, 13, 24, 44.

Given an array containing the first three numbers of a Tribonacci sequence, and an integer representing the length of the sequence, return an array containing the sequence of the given length.

• Your function should handle sequences of any length greater than or equal to zero.
• If the length is zero, return an empty array.
• Note that the starting numbers are part of the sequence.

--hints--

tribonacciSequence([0, 0, 1], 20) should return [0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136, 5768, 10609, 19513].

assert.deepEqual(tribonacciSequence([0, 0, 1], 20), [0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 81, 149, 274, 504, 927, 1705, 3136, 5768, 10609, 19513]);

tribonacciSequence([21, 32, 43], 1) should return [21].

assert.deepEqual(tribonacciSequence([21, 32, 43], 1), [21]);

tribonacciSequence([0, 0, 1], 0) should return [].

assert.deepEqual(tribonacciSequence([0, 0, 1], 0), []);

tribonacciSequence([10, 20, 30], 2) should return [10, 20].

assert.deepEqual(tribonacciSequence([10, 20, 30], 2), [10, 20]);

tribonacciSequence([10, 20, 30], 3) should return [10, 20, 30].

assert.deepEqual(tribonacciSequence([10, 20, 30], 3), [10, 20, 30]);

tribonacciSequence([123, 456, 789], 8) should return [123, 456, 789, 1368, 2613, 4770, 8751, 16134].

assert.deepEqual(tribonacciSequence([123, 456, 789], 8), [123, 456, 789, 1368, 2613, 4770, 8751, 16134]);

--seed--

--seed-contents--

function tribonacciSequence(startSequence, length) {

  return length;
}

--solutions--

function tribonacciSequence(startSequence, length) {
  if (length === 0) return [];
  if (length === 1) return [startSequence[0]];
  if (length === 2) return [startSequence[0], startSequence[1]];
  if (length === 3) return [...startSequence];

  const sequence = [...startSequence];
  while (sequence.length < length) {
    const nextValue = sequence[sequence.length - 1] + sequence[sequence.length - 2] + + sequence[sequence.length - 3];
    sequence.push(nextValue);
  }
  return sequence;
}