Perfect solution of Remove Duplicates From Sorted Array
Author Xin Zhou
Random Array Generation
Description: Given an integer n, write a function to return an array of
size n, containing each of the numbers from 0 to n - 1 in a random
order. The number may not repeat and each number must show up exactly
once.

Example:
n = 4	output: 2, 0, 1, 3
2, 0, 0, 1 is not a valid array since 0 is duplicated and the 3 does not
appear