mjstromberg

function getUniqueSteps(n, stepSizes = []) {
  return stepSizes.reduce((sum, stepSize) => {
    if (n < stepSize) {
      return sum;
    } else if (stepSize === n) {
      return sum + 1;
    } else {
      return sum + getUniqueSteps(n - stepSize, stepSizes);
    }
  }, 0);

mjstromberg

function getUniqueStepsByOneOrTwo(n) {
  if (n < 0) {
    return 0;
  } else if (n === 0) {
    return 1;
  } else {
    return getUniqueStepsByOneOrTwo(n - 1) + getUniqueStepsByOneOrTwo(n - 2);
  }
}