Why WA 15? Help me please.

import java.util.Arrays;
import java.util.Scanner;


public class Timus1579 {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        int n=in.nextInt(),r=in.nextInt();
        Shub[] a=new Shub[n];
        Xod[] x=new Xod[n];
        int ix=1,im=0,gt=0;
        a[0]=new Shub(in.nextInt(),0);
        x[0]=new Xod(a[0].size);
        for(int i=1; i<n; i++){
            a[i]=new Shub(in.nextInt(),i);
            if(x[im].size+r<a[i].size){
                x[im].size=a[i].size;
                x[im].amount++;
                a[i].num=im;
                im=(im+1)%ix;
            }else{
                a[i].num=ix;
                x[ix]=new Xod(a[i].size);
                ix++;
            }
        }
        System.out.println(ix);
        Arrays.sort(a);

        for(int i=0; i<ix; i++){
            System.out.print(x[i].amount+" ");
            while((gt<n)&& (a[gt].num==i)){
                System.out.print((a[gt].num2+1)+" ");
                gt++;
            }
            System.out.println();
        }
    }
}
class Shub implements Comparable{
    int num,num2,size;

    public Shub(int s, int n) {
        num=0;
        size=s;
        num2=n;
    }

    public int compareTo(Object o) {
        Shub a=(Shub)o;
        if(num==a.num){
            return num2-a.num2;
        }else return num-a.num;
    }
}
class Xod{
    int size,amount;
    public Xod(int i) {
        size=i;
        amount=1;
    }
}