7.29 第二题   
public class Test {  public static void setAdd(Set<Integer> set,Integer i){  if(!set.add(i)){
            set.remove(i);  setAdd(set,i<<1);  }
    }  public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);  int n = scanner.nextInt();   Integer[] array = new Integer[n];  for (int i = 0; i < array.length; i++) {
            array[i] = scanner.nextInt();  }
        LinkedHashSet<Integer> res = new LinkedHashSet<>();  for (int i = 0; i < array.length; i++) { setAdd(res,array[i]);  }
        Iterator<Integer> iterator = res.iterator(); while (iterator.hasNext()){
            System.out.print(iterator.next()); if(iterator.hasNext())System.out.print(" "); }
    }
}