从List <>中动态删除并添加另一个字母，并保持字母顺序

Question

I have this predefined string array :

string[] SkippedAreasArray = new string[] {"A", "B", "C", "D", "E", "F", "G",
            "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q"};

And according to an user input I populate a List<string> like this :

List<String> UsedAreas = new List<String>();
int RangeOfInput = (int)entity.AreasCnt;
UsedAreas = SkippedAreasArray.ToList().GetRange(0, RangeOfInput);

Also from an user input I get another string containing non-duplicated letters from A to Q (like in SkippedAreasArray ).

The array is formed like this :

SkippedAreasFromForm = (txtSkippedAreas.Text).ToUpper().Split(',');

What I do is first - sorting the SkippedAreasFromForm :

Array.Sort<string>(SkippedAreasFromForm);

And then I need the following :

foreach (string tempAreaValue in SkippedAreasFromForm)
{
    if (UsedAreas.Contains(tempAreaValue))
    {

    }
    else 
    { 

    }
}

if the List<> UsedAreas contains the letter that is checked I want to remove this letter from the List and at the same time to add the next letter that follows in alphabetical order.

PS

I see now that my goal is not clear here so I'll explain the meaning of this :

SkippedAreasFromForm is an user input that should be validated and that's the idea to want this algorithm. If in some case if (UsedAreas.Contains(tempAreaValue)) returns false then the input is wrong and I need to return error message.

Answer 1

You can use LINQ to Objects to achieve that without looping:

UsedAreas = SkippedAreasArray.Except(SkippedAreasFromForm)
                             .OrderBy(e => e)
                             .Take(RangeOfInput)
                             .ToList();

It's taking RangeOfInput elements from SkippedAreasArray that are not in SkippedAreasFromForm . Result is List<string> .

Update

You can check your error message condition that way:

if(SkippedAreasFromForm.Except(SkippedAreasArray.Take(RangeOfInput)).Any())
{
    // incorrect user input
}

Answer 2

IEnumerable<string> usedAreas = SkippedAreasArray.Take(RangeOfInput);
IEnumerable<string> skippedAreasFromForm = (txtSkippedAreas.Text).ToUpper()
    .Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
IEnumerable<string> invalids = skippedAreasFromForm.Except(usedAreas);
if (invalids.Any())
    MessageBox.Show(string.Format("These are invalid: [{0}]", 
        string.Join(",", invalids.OrderBy(sa => sa))));