function singleNumber(numbers: number[]): number {

  let filteredNumbers = numbers;

  for (let i = 0; i < numbers.length; i++) {
    if (numbers.indexOf(numbers[i], i + 1) != -1) {
      filteredNumbers = filteredNumbers.filter( value => value !== numbers[i])
    }
  }

  return filteredNumbers[0]
}

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