Remove Repeats

You get an ArrayList of integers nums. Some values may appear more than once.

Return a new ArrayList that has each value only once.

Keep the first copy of each value and drop the later ones. The values stay in the order they first appear in nums.

Example 1:

Input: nums = [3, 1, 3, 2, 1]
Output: [3, 1, 2]
Explanation: The second 3 and the second 1 are repeats.
They are dropped, and 3, 1 and 2 stay in their order.

Example 2:

Input: nums = [6, 6, 6, 6]
Output: [6]
Explanation: Only the first 6 stays.

Example 3:

Input: nums = [4, 9, 2]
Output: [4, 9, 2]
Explanation: No value repeats, so every number stays.

Constraints:

• nums has at least one number.
• Every number is between -10⁹ and 10⁹.