code for the finding the 2nd most occurring letter present in the string

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Runnersup {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int zz=sc.nextInt();
        sc.nextLine();
        for (int i = 0; i < zz; i++) {
            String s[]=sc.nextLine().split("");
            Arrays.sort(s);
            HashMap<Integer,String> m=new HashMap<>();
            String ss=s[0];
            int c=0;
            int j=-1;
            while(++j<s.length-1) {
                if (j < s.length && ss.equals(s[j])) {
                    ++c;
                } else if (j < s.length && !ss.equals(s[j])) {
                    m.put(c, s[j - 1]);
                    ss = s[j];
                    c = 1;
                } else
                    m.put(c, s[j - 1]);
            }
            if(m.size()==1)
                System.out.println("-1");
            else{
                int f=1;
                for (Map.Entry<Integer,String> mm: m.entrySet()){
                    if (f==m.size()-1){
                        System.out.println(mm.getValue());
                        break;
                    }
                    ++f;
                }
            }
        }
    }


}

Try commenting your code a little bit, it is illegible