设计一个方法，删除一个有N个元素的数组A中所有的重复元素，返回仍留在数组A中的元素个数。函数的时间复杂度必须为O(NlogN)（提示：用快速派讯作为一个预处理步骤）。-Design A method, delete A N element of the array of all the elements of A repeat, returns to remain in A number of elements in the array. The time complexity must for O (NlogN) (hint: use the rapid pie-as a preprocessing step).