AdventOfCode 2018 Day 05

void Main()
{
    ///TEST PART
    Debug.Assert(GetAnswerA("dabAcCaCBAcCcaDA") == 10);
    Debug.Assert(GetAnswerB("dabAcCaCBAcCcaDA") == 4);

    var aoc = new AdventOfCode(2018, 5);

    aoc.SubmitAnswer(GetAnswerA(aoc.InputLines[0]), Part.A);
    aoc.SubmitAnswer(GetAnswerB(aoc.InputLines[0]), Part.B);
}

public int GetAnswerB(string input)
{
    //keep track of the shortest length found
    int best = int.MaxValue;

    //remove each letter in the alphabet
    for (char i = 'a'; i <= 'z'; i++)
    {
        //remove the upper and lower
        var result = input.Replace(i.ToString(), "");
        result = result.Replace(i.ToString().ToUpper(), "");

        //get the resulting length
        best = Math.Min(GetAnswerA(result), best);
    }

    return best;
}

public int GetAnswerA(string result)
{
    //to array, so we can change values
    var linked = result.ToArray();

    //keep track if the lenght changed
    int len = 0;

    //keep repeating while the length changes
    while (len != linked.Length)
    {
        //update length
        len = linked.Length;

        //move over the array
        for(int i = 0; i < linked.Length - 1; i++)
        {
            int j = i + 1;
            //check inside the array?, are the upper and lower diff is 32 in dec)
            while(i >= 0 && j < linked.Length && Math.Abs(linked[i] - linked[j]) == 32)
            {
                //replate by null
                linked[i--] = '\0';  //move i back
                linked[j++] = '\0'; //move j forward (not on nulls anymore)
            }
            i = j -1; //continue where we were
        }

        //new array
        linked = linked.Where(x => x != '\0').ToArray();
    }

    return linked.Length;
}