左右指针法容易出现问题的地方是一趟快速排序相遇时的处理方式
如果参考在末尾，要先从左走
如果参考在数组头部，要先从右走

参考在数组头部，要先从右走

    private static int partition(int[] array, int left, int right) {
        int key = array[left];
        int index = left;
        while (left < right) {

            while (left < right && array[right] <= key) {
                --right;
            }

            while (left < right && array[left] >= key) {
                ++left;
            }

            swap(array, left, right);
        }
        swap(array, right, index);
        return right;
    }

    private static void swap(int[] cost, int i, int j) {
        int temp = cost[i];
        cost[i] = cost[j];
        cost[j] = temp;
    }

参考在末尾，要先从左走

    private static int partition2(int[] array, int left, int right) {
        int key = array[right];
        int index = right;
        while (left < right) {

            while (left < right && array[left] <= key) {
                ++left;
            }

            while (left < right && array[right] >= key) {
                --right;
            }

            swap(array, left, right);
        }
        swap(array, left, index);
        return left;
    }

参考：
https://www.jianshu.com/p/bb41e3be09ba