Given an integer array, nums, sort it in ascending order and return the sorted array.

You must implement the sorting algorithm yourself; do not use any built-in sorting functions. The solution must run in $O(n \log n)$ time and use the minimum possible extra space.

Constraints:

• $1 \leq$ nums.length $\leq 10^3$

• $-10^3 \leq$ nums[i] $\leq 10^3$ ...