public static void quickSort(int[] arr, int start, int end) {
  if (start < end) {
   int key = arr[start];
   int right = start;
   int left = end;
   while (right < left) {
    while (right < left && arr[left] > key) {
     left --;
    }
    if (right < left) {
     arr[right] = arr[left];
    }
    while (right < left && arr[right] <= key) {
     right ++;
    }
    if (right < left) {
     arr[left] = arr[right];
    }
   }
   arr[right] = key;
   quickSort(arr, start, right-1);
   quickSort(arr, left+1, end);
  }
 }
 

                int k = 4;
  for (int i=arr.length-1; i>=arr.length-k; i--) {
   System.out.println(arr[i]+"  ");
  }

public static int[] selectSortK(int[] arr, int k) {
  if(arr == null || arr.length == 0) {
   return null;
  }
  int[] newArr = new int[k];
  List<Integer> list = new ArrayList<Integer>();//記錄每次最大數的下標
  for (int i=0; i<k; i++) {
   int maxValue = Integer.MIN_VALUE; //最大值
   int maxIndex = i;
   for (int j=0; j<arr.length; j++) {
    if (arr[j] > maxValue && !list.contains(j) ) {
     maxValue = arr[j];
     maxIndex = j;
    }
   }
   if (!list.contains(maxIndex)) {//如果不存在，就加入
    list.add(maxIndex);
    newArr[i] = maxValue;
   }
  }
  return newArr;
 }