using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string s = "((100 0, 101 0, 101 1, 100 1, 100 0)        ,  (100.2 0.2, 100.8 0.2, 100.8 0.8, 100.2 0.8, 100.2 0.2))";

        s = Regex.Replace(s, " *, *", ",");

        Console.WriteLine(s);

    }

}