Determine if all characters in a string are the same

Question

I have a situation where I need to try and filter out fake SSN numbers. From what I've seen so far if they are fake they're all the same number or 123456789. I can filter for the last one, but is there an easy way to determine if all the characters are the same?

Answer 1

return (ssn.Distinct().Count() == 1)

Answer 2

This method should do the trick:

public static bool AreAllCharactersSame(string s)
{
    return s.Length == 0 || s.All(ch => ch == s[0]);
}

Explanation: if a string's length is 0, then of course all characters are the same. Otherwise, a string's characters are all the same if they are all equal to the first.