Question

Is it possible to write a regular expression to check whether all numbers of specific 10 digit number occured up to 3 times?
for example return value for Regex.IsMatch("xxxx", "4433425425") is false.
and for Regex.IsMatch("xxxx", "4463322545") is true. what is xxxx?
in the first one i have 4 occurrence of digit 4 and in second one non of digits occurred more than 3 times.

Answer 1

Will match any digit that has four or more instances

 string found =  Regex.Match(s,@"(\d).*\1.*\1.*\1").Groups[1].Value;

Just an example of how to use it

static void Main( string[] args )
{
     string fail = "1234567890";
     string s = "1231231222";
     string mTxt = @"(\d).*\1.*\1.*\1";
     Console.WriteLine( Regex.Match(s,mTxt).Success);
     Console.WriteLine(Regex.Match(fail, mTxt).Success);
}

---

Baised on @Brads Comments below use

([0-9]).*\1.*\1.*\1