i慢指针，j快指针。由于原排列已经排序，所以i从0开始，j从1开始，如果i的值等于j的值，则j后移一位。如果i不等于j的值，则i后移一位，并且用nuns[i]记录此时nums[j]的值。然后j继续后移。

//Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length. //Do not allocate extra space for another array, you must do this by ...