Надеюсь, ответа Рад будет достаточно для вашего вопроса.
Вот полный рабочий код:
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
class Program
{
static void Main()
{
List<int> list = new List<int>();
Console.WriteLine("Number: ");
int num = int.Parse(Console.ReadLine());
while (num > 0)
{
list.Add(num % 10);
num /= 10;
}
list.Reverse();
var distinct = list.GroupBy(x => x)
.Where(y => y.Count() == 1) //It'll count numbers which have single number sequence like 1 2 3 ,etc. but for double number sequence like 22 33 44 ,etc. change Count() == 2
.Select(y => y.Key).ToList();
foreach (object value in distinct)
Console.Write("{0}", value);
Console.WriteLine();
Console.ReadLine();
}
}