Remove duplicates recursively


Eliminate the character and it's pair when they are same. Repeat it until there is no adjacent duplicates in the string
Sample input: 
 aabcddceffgge
Sample output:
bccee
b


Code:

import java.util.*;

public class Program3 {
  
    public static void removeDuplicates(StringBuilder s){
      
        int len = s.length();
        int i=0;
      
        while(i<len-1){
            if(s.charAt(i) == s.charAt(i+1)){
                s.delete(i, i+2);
                len-=2;
            }
            else{
                i++;
            }
        }
      
        System.out.println(s);
      
        if( isDuplicatesPresent(s))
            removeDuplicates(s);
      
    }
  
    public static boolean isDuplicatesPresent(StringBuilder s){
      
        boolean present = false;
      
        HashSet<Character> set = new HashSet<Character>();
      
        int len = s.length();
      
        for(int i=0; i<len; i++){
            if(!set.add(s.charAt(i)) && s.charAt(i) == s.charAt(i-1)){
                present = true;
                break;
            }
        }
      
        return present;
    }
  
    public static void main(String[] args){
        StringBuilder s;
        Scanner in = new Scanner(System.in);
      
        s = new StringBuilder(in.nextLine());
      
        removeDuplicates(s);
      
    }

}


Input:
aabcddceffgge


Output:
bccee
b



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