Counting distinct digits

Question

Is there any efficient way to find out the count of distinct digits from a given number in constant time or O(Logn)?

Suppose n = 1234 the count should be 4 (As there are 4 distinct digits)

if n = 1121 the count should be 2 (As there are 2distinct digits i.e 1, 2)

Constraint: 0 <= n <= 1000000007

Answer 1

Pseudo-code:

int DistinctDigits(int n)
{
    int result = 0;
    bool[10] digitFound = {false};

    while (n > 0)
    {
      d = n % 10;
      n = n / 10;

      if (!digitFound[d])
      {
        result++;
        digitFound[d] = true;
      }
    }
    return result;
}

Note that you have to think about what to do with leading zeroes (including when n == 0).