Remove duplicate char from String without using array in Java

Question

Solution:

public class RemoveDuplicateInString {

    public void removeDuplicate(String s){
        System.out.println("Before::"+s);
        int len = s.length();
        for(int i=0;i<len-1;i++){
            char c = s.charAt(i);
            String preString = s.substring(0,i+1);
            String temp = s.substring(i+1);
            temp = temp.replaceAll(""+c, "");
            System.out.println("....::"+temp);
            s =  preString + temp;
            len = s.length();
        }
        System.out.println("After::"+s);
    }

    public static void main(String args[]){
         RemoveDuplicateInString duplicate  = new RemoveDuplicateInString();
         duplicate.removeDuplicate("adfahagabfgdbah");
    }

}

Answer 1

This code is highly ineffective, as it uses lot of string concatenation, and temporary strings, that's for StringBuilder is designed for.

public class RemoveDuplicateInString {

    public String removeDuplicate(String s){
        StringBuilder sb = new StringBuilder(s.length());
        int len = s.length();

        for(int i=0;i<len;i++){
            char c = s.charAt(i);
            if(sb.indexOf(String.valueOf(c))==-1)
                sb.append(c);
        }

        return sb.toString();
    }

    public static void main(String args[]){
        RemoveDuplicateInString duplicate  = new RemoveDuplicateInString();
        String s = "adfahagabfgdbah";

        System.out.println("Before::"+s);
        String s2 = duplicate.removeDuplicate(s);
        System.out.println("After::"+ s2);
    }
}

This will have O(n* log(n)) complexity, or O(n*m), where m is count of unique characters.