Combination Sum

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.

Latest Source Code:
Github: CombinationSum.java

Output:

When k=3, n=7
Combination: [[1, 2, 4]]

When k=3, n=9
Combination: [[1, 2, 6], [1, 3, 5], [2, 3, 4]]