String : Remove duplicate characters

Question : Remove Duplicate characters from a string.

Solution :

Basically the solution involves counting the occurences of characters in the string .

First solution uses an in-built Hashtable :

    public static String removeDuplicateCharHash(String ip){
        Hashtable<Character, Integer> ht = new Hashtable<Character, Integer>();
        String op = new String("");
        for(int i=0;i<ip.length();i++){
            Character ch = ip.charAt(i);
            if (! ht.containsKey(ch))
            { op = op + ch; ht.put(ch, new Integer(1)); }
        }
        return op;
    }
   
Second Solution uses a bit vector which is used as a hastable:

    public static String removeDuplicateChar(String ip){
// Initialize the bit vector  
    int ht[] = new int[256];
        for (int i=0;i<256;i++)
            ht[i] = 0;
     
  String op = "";
       
        for (int i=0;i<ip.length();i++){
            char ch = ip.charAt(i);
            if (ht[ch] == 0)
            {op = op + ch; ht[ch]++;}
        }
       
        return op;
    }