Finding the Kth smallest string

import java.util.Vector;
import java.util.*;

public class Test {

    static Scanner sc = new Scanner(System.in);

    public static void swap(char ch[],int i,int j) {
        char temp = ch[i];
        ch[i] = ch[j];
        ch[j] = temp;
    }

    public static void findingAllRearrangements(char ch[],int n,Vector<String> v,int itr){
        if(itr==n-1){
            String s = "";
            for(char i : ch) {
                s+=i;
            }
            v.add(s);
            return;
        }
        HashSet<Character> hs = new HashSet<Character>();
        for(int i=itr;i<n;i++) {
            if(!hs.contains(ch[i])) {
                hs.add(ch[i]);
                swap(ch,itr,i);
                findingAllRearrangements(ch,n,v,itr+1);
                swap(ch,itr,i);
            }
        }
    }

    public static String findingKthSmallest(int n, int k, String s){
        char ch[] = s.toCharArray();
        Vector<String> v = new Vector<String>();
        findingAllRearrangements(ch,n,v,0);
        Collections.sort(v);
        if(k<=v.size()) {
            return v.get(k-1);
        }
        return "-1";
    }

    public static void main(String[] args) {
        int n = sc.nextInt();
        int k = sc.nextInt();
        String s = sc.next();

        System.out.println(findingKthSmallest(n,k,s));
    }

}