JeffZ20190821.cs

void Main()
{
       var myValues = new MyValues("abc,a,def,a,def,abcd,dd");
       foreach (var item in myValues)
       {
              System.Console.WriteLine(item);
       }
       
       System.Console.WriteLine("another test:");
       
       myValues = new MyValues("abe,b,def,a,def,abcd");
       foreach (var item in myValues)
       {
              System.Console.WriteLine(item);
       }
       
       System.Console.WriteLine("test3:");

       myValues = new MyValues("z,z");
       foreach (var item in myValues)
       {
              System.Console.WriteLine(item);
       }

       System.Console.WriteLine("test4:");

       myValues = new MyValues("M");
       foreach (var item in myValues)
       {
              System.Console.WriteLine(item);
       }
}


public class MyValues : IEnumerable<String> {

       private readonly static String[] allWords = new String[50];
       private static int wordsCount = 0;
       private readonly int[] _values;

       public MyValues(string values) {
              _values = parse(values);
       }
       
       public IEnumerator<string> GetEnumerator() {
              return _values.Select(w => allWords[w]).GetEnumerator();
       }
       
       IEnumerator IEnumerable.GetEnumerator() {
              return GetEnumerator();
       }
       
       private int[] parse(String values) {
              
              HashSet<int> words = new HashSet<int>();
              
              int start = 0;
              for(int pos = 0; pos < values.Length; pos++) {
                     if(values[pos] != ',' && pos != values.Length - 1) continue;
                     
                     var wordPosition = GetValue(values, start, (pos == values.Length - 1 ? pos + 1 : pos) - start);
                     if (wordPosition.Item2) // new word, the old indexes larger than the current one, needs to increase the index value
                     {
                           HashSet<int> newWords = new HashSet<int>();
                           foreach(var w in words) {
                                  if(w >= wordPosition.Item1)
                                  newWords.Add(w + 1);
                                  else
                                  newWords.Add(w);
                           }
                           words = newWords;
                     }
                     
                     words.Add(wordPosition.Item1);
                     
                     start = pos + 1;
              }
              
              return words.OrderBy(w => w).ToArray();
       }
       
       private Tuple<int, bool> GetValue(String values, int start, int length) {
              
              for(int i = 0; i < wordsCount; i++) { // could use binary search here
                     String word = allWords[i];
                                         
                     int result = Compare(word, values, start, length);

                     if (result == 0) {
                           return Tuple.Create(i, false); // it's not a new word
                     }

                     if (result < 0) {
                           AddWord(values, start, length, i);
                           return Tuple.Create(i, true); // it's a new word, return the index of it
                     }
              }
              AddWord(values, start, length, wordsCount);
              return Tuple.Create(wordsCount - 1, true); // it's a new word, return the index of it
       }

       private void AddWord(String values, int start, int length, int position) {
              String word = values.Substring(start, length);
              for(int i = wordsCount - 1; i >= position; i--) {
                     allWords[i + 1] = allWords[i];
              }
              allWords[position] = word;
              wordsCount++;
       }
       
       private int Compare(String sample, String values, int start, int length) {
              
              for(int i = 0; i < (sample.Length > length ? length : sample.Length); i++) {
                     int result = values[i + start].CompareTo(sample[i]);
                     if(result == 0) continue;
                     return result;
              }
              return length.CompareTo(sample.Length);
       }
}