Scan document - practice code - need to review more

ScanDocument_practice.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text; 

class ScanDocument {
   static void Main(string[] args) {
      //string s = WordCountEngine("practice makes perfect, ", " !.");  // customize the delimiters here if necessaray 
      //Console.WriteLine(s);

       //RunTestcaseOnSplit();
       RunTestcase(); 
   }
   
   public static void RunTestcase()
   {
       var result = WordCountEngine(" a,b,c,a a", " ,"); 
   }

   public static void RunTestcaseOnSplit()
   {
       var result = splitMethod("  a,b,c", " ,");
       Debug.Assert(result[0].CompareTo("a") == 0); 
   }

  
   /// <summary>
   /// minimum run time O(N) + O(NM), N is word's length, and M is specialDelimeters' length 
   /// </summary>
   /// <param name="words"></param>
   /// <param name="specialDelimeters"></param>
   /// <returns></returns>
   public static string WordCountEngine(string words, string specialDelimeters)
   {
      IList<string> data = new List<string>(); 
      
      if(words == null || words.Length ==0)
      {
         return string.Empty;
      }
      
      //var specailDelimters = " -;";
      var split = splitMethod(words, specialDelimeters);  // O(N)
      
      var raw = new Dictionary<string, int>(); 
      
      foreach(var s in split)
      {
         if(raw.ContainsKey(s))
         {
            raw[s]++; 
         }
         else
         {
            raw.Add(s,1);
         }
      }
      
      // depending on dictionary
      // time O(NlogN)      
      var sorted =  from entry in raw orderby entry.Value descending select entry; 
 
      data.Add("{ ");
      
      int length = sorted.Count(); 
      int index = 0; 

      foreach(var item in sorted)
      {
         StringBuilder temp = new StringBuilder(); 

         temp.Append(item.Key + ": " + item.Value); 
         
          if(index < length - 1)
          {
             temp.Append(",");
          }
         
         data.Add(temp.ToString()); 

         index ++; 
      }
      
      data.Add(" }");
      
      return string.Join("", data.ToArray()); 
   }   
   
   /// <summary>
   /// delimter =" ;-/"
   /// delimiter string length is m
   /// n * m , n is string s's length
   /// algorithm time complexity is O(nm) 
   /// 
   /// actually C# string.Split(Char[])
   /// </summary>
   /// <param name="s"></param>
   /// <param name="delimiters"></param>
   /// <returns></returns>
   private static string[] splitMethod(string s, string delimiters)
   {
      IList<string> output = new List<string>();
      
      if(s == null || s.Length == 0)
      {
         return new string[0]; 
      }
      
      int length = s.Length; 
      int start = 0; 
      int end   = 0; 
      
      for(int i = 0; i < length ; i++)
      {
         var current = s[i];
         
         var startChar = s[start];         
         
          // continue to skip delimiter char if need
         if(delimiters.IndexOf(startChar) >= 0)
         {
             start = i; 
             if(end < start)
             {
                end = start; 
             }
         }
         
         if(delimiters.IndexOf(current) >= 0)
         {
            end = i; 
            
            // output the word, s[end] is delimiter 
            if(end - start > 0)
            {
                output.Add(s.Substring(start, end - start)); // minus 1, checking               
                
                start = end + 1; 
            }                                                 
         }
      }

      // edge case
      if (delimiters.IndexOf(s[start]) < 0 )
      {
          output.Add(s.Substring(start, length - start)); 
      }

      return output.ToArray(); 
   }   
}