function increment ( numbers ) {

  let iterator = numbers.length - 1

  while ( iterator >= 0 ) {
    let num = numbers[ iterator ]
    num++

    if (num > 0 && num <= 9) {
      numbers[ iterator ] = num
      break
    } else {
      numbers[ iterator ] = 0
      if ( iterator == 0 ) { // For the [ 9, 9, 9 ] case
        numbers.unshift(1)
        break
      }
      iterator--
    }
  }
  return numbers
}