将 Long 转换为整数数组

Question

How could I convert a long such as:

123456789123456789

into:

[1,2,3,4,5,6,7,8,9,1,2,3,4,5,6,7,8,9]

I ask because I need a way to iterate through a Long in C sharp, but Long apparently doesn't use [ ] for arrays, so I can't seem to access each number.

Answer 1

This is pretty crude, but you could convert the long into a string and then break it up into single digits and convert them back to integers like this

var digits = 123456789123456789L.ToString().Select(d => int.Parse(d.ToString()));

To convert back from an array to a long, you can do

var longFromDigits = digits.Aggregate(0L, (s, d) => s * 10 + d);

Answer 2

If you don't want to operate with string s you can just loop over digits with a help of modulo arithmetics:

public static int[] Digits(long value) {
  if (value == 0)
    return new int[] { 0 };

  List<int> result = new List<int>();

  for (; value != 0; value /= 10)
    result.Add((int)Math.Abs(value % 10));

  result.Reverse();

  return result.ToArray();
}

then

int[] digits = Digits(123456789123456789L);

Edit: All you have to do is to Aggregate the digits to have the long back:

int[] digits = new [] { 1, 2, 3};

long result = digits.Aggregate(0L, (s, a) => s * 10 + a);