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Given an array of distinct integers nums and a target integer target, return the number of possible combinations that add up to target.
The answer is guaranteed to 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 <= 2001 <= nums[i] <= 1000- All the elements of
numsare 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?