function flattenOneLevel(array: (number | number[])[]): (number|number[])[] {
  const length = array.length;
  if (length === 0) return [];
  const result = [];

  for (let i = 0; i <= length - 1; i++) {
    let element = array[i];

    if (!Array.isArray(element)) {
      result.push(element);
      continue;
    }

    for (let j = 0; j <= element.length - 1; j++) {
      result.push(element[j]);
    }
  }

  return result;
}

// No modificar: necesario para evaluar el resultado.
export { flattenOneLevel };