using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var testInput = new[] { new TestInput("111222", 2),

                                new TestInput("1002345", 6),

                                new TestInput("000000", 1)};

​

        foreach( var item in testInput )

        {

            var actual = GetDigitCount(item.Input);

            Console.WriteLine($"{item.Input,10} | {actual,2} | expected: {item.Expected}");

        }

    }

    public static int GetDigitCount(ReadOnlySpan<char> input)

    {

        HashSet<char> hs = new();

        foreach(var c in input) if( char.IsDigit(c) ) hs.Add(c) ;

        return hs.Count;

    }

}

​

public record struct TestInput(string Input, int Expected);