Question

I want to extract unique characters from a string. For example:- 'AAABBBBBCCCCFFFFGGGGGDDDDJJJJJJ' will return 'ABCFGDJ'

I have tried below piece of code but now I want to optimize it.
Please suggest if anyone knows.

static string extract(string original)
 {
        List<char> characters = new List<char>();   
        string unique = string.Empty; 
        foreach (char letter in original.ToCharArray())    
         {  
             if (!characters.Contains(letter))   
             {      
                  characters.Add(letter);   
              }            
          }  
        foreach (char letter in characters)
        {  
              unique += letter;    
         }     
     return unique;
 } 

Answer 1

I don’t know if this is faster, but surely shorter

string s = "AAABBBBBCCCCFFFFGGGGGDDDDJJJJJJ";
var newstr = String.Join("", s.Distinct());