Codewars Test 3

codewarsThree

function combineValues(data) {
  // compute the value of the last 3 vals
  return getLastThree(data).reduce((a, b) => {
    return a + b;
  }, 0);
}

function getLastThree(data) {
  // if the length is 3 we don't need to pull any specific locations as we are computing against all of these
  if (data.length > 3) {
    return [data[data.length -1 ], data[data.length - 2], data[data.length -3]];
  }
  else return data;
}

function tribonacci(signature, n) {
  // first add together the three digits of signature to our new array to avoid mutation
  let newSignature = [...signature];
  // declare storage for our new values that will be computed
  let next;
  // compute n new values
  for (var i = 0; i < n-3; i++) {
    next = combineValues(newSignature)
    newSignature.push(next);
  }
  // return our new array
  if (n === 0) {
    return [];
  } else if (n <= 3) {
    // if n is 3 or lower return that many locations of signature
    // [0, 0, 1], 2
    // [0, 1, 2]
    return signature.filter((num, i) => {
      if (i < n) {
        return true;
      }
    });
  } else {
    return newSignature;
  }
}

console.log(tribonacci([1,1,1],10));
// [1,1,1,3,5,9,17,31,57,105]
console.log(tribonacci([0,0,1], 10));
// [0,0,1,1,2,4,7,13,24,44]
console.log(tribonacci([0,1,2], 1));