How can you remove duplicate characters in a string?

Question

I have to implements a function that takes a string as an input and finds the non-duplicate character from this string.

So an an example is if I pass string str = \"

Answer 1

Revised version of the first answer i.e: You don't need ToCharArray() function for this to work.

public static string RemoveDuplicates(string input)
{
    return new string(input.Distinct().ToArray());
}

Answer 2

My answer in java language.
Posting here so that you might get a idea even it is in Java language.Algorithm would remain same.

public String removeDup(String s)
  {
    if(s==null) return null;
    int l = s.length();
    //if length is less than 2 return string
    if(l<2)return s;
    char arr[] = s.toCharArray();

    for(int i=0;i<l;i++)
    {
      int j =i+1; //index to check with ith index
      int t = i+1; //index of first repetative char.

      while(j<l)
      {
        if(arr[j]==arr[i])
        {
          j++;

        }
        else
        {
          arr[t]=arr[j];
          t++;
          j++;
        }

      }
      l=t;
    }

    return new String(arr,0,l);
  }

Answer 3

A Linq approach:

public static string RemoveDuplicates(string input)
{
    return new string(input.ToCharArray().Distinct().ToArray());
}

Answer 4

Below is the code to remove duplicate chars from a string

        var input = "SaaSingeshe";
        var filteredString = new StringBuilder();
        foreach(char c in input)
        {
            if(filteredString.ToString().IndexOf(c)==-1)
            {
                filteredString.Append(c);
            }
        }
        Console.WriteLine(filteredString);
        Console.ReadKey();

Answer 5

For arbitrary length strings of byte-sized characters (not for wide characters or other encodings), I would use a lookup table, one bit per character (32 bytes for a 256-bit table). Loop through your string, only output characters that don't have their bits turned on, then turn the bit on for that character.

string removedupes(string s)
{
    string t;
    byte[] found = new byte[256];
    foreach(char c in s)
    {
        if(!found[c]) {
            t.Append(c);
            found[c]=1;
        }
    }
    return t;
}

I am not good with C#, so I don't know the right way to use a bitfield instead of a byte array.

If you know that your strings are going to be very short, then other approaches would offer better memory usage and/or speed.

Answer 6

It sounds like homework to me, so I'm just going to describe at a high level.

• Loop over the string, examining each character
• Check if you've seen the character before
  • if you have, remove it from the string
  • if you haven't, note that you've now seen that character