Given an array of distinct integers `nums` and a target integer `target`, return the number of possible combinations that add up to `target`.

The test cases are generated so that the answer can fit in a 32-bit integer.

Example 1:

    Input: nums = [1,2,3], target = 4
    Output: 7
    Explanation:
    The possible combination ways are:
    (1, 1, 1, 1)
    (1, 1, 2)
    (1, 2, 1)
    (1, 3)
    (2, 1, 1)
    (2, 2)
    (3, 1)
    Note that different sequences are counted as different combinations.

Example 2:

    Input: nums = [9], target = 3
    Output: 0

Constraints:

- `1 <= nums.length <= 200`
- `1 <= nums[i] <= 1000`
- All the elements of `nums` are unique.
- `1 <= target <= 1000`

Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?