string a = "123,123,12,124,125,124,";

        string[] result = a.Split(',').Distinct().ToArray();

        string b = string.Join(",", result);

//结果b等于：123,12,124,125,

------解决方案--------------------
C# code
            string str="123,123,12,124,125,124,";
            Regex reg = new Regex(@"((\d+,).*?)\2");
            while (str != (str = reg.Replace(str, "$1"))) ;
            Console.WriteLine(str);

------解决方案--------------------
探讨


引用:
C# code
while (str != (str = reg.Replace(str, "$1"))) ;
这是个什么循环？


------解决方案--------------------
string a = "123,123,12,124,125,124,";
           string[] str = a.Split(',');

           IEnumerable<string> ling = (from b in str select b).Distinct();
           StringBuilder strbuil = new StringBuilder(100);
           foreach (string s in ling)
           {
               strbuil.Append(s);
           }