# Combination Sum III

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.

Example 1:

Input: k = 3, n = 7

Output:

```
[[1,2,4]]
```

Example 2:

Input: k = 3, n = 9

Output:

```
[[1,2,6], [1,3,5], [2,3,4]]
```

```
public class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> result = new ArrayList<>();
if (k <= 0 || n <= 0) {
return result;
}
helper(k, n, result, new ArrayList<Integer>(), 1);
return result;
}
void helper(int k, int n, List<List<Integer>> result, List<Integer> list, int start) {
if (n < 0 || list.size() > k) {
return;
}
if (n == 0 && list.size() == k) {
result.add(new ArrayList<>(list));
return;
}
for (int i = start; i <= 9; i++) {
list.add(i);
helper(k, n - i, result, list, i + 1);
list.remove(list.size() - 1);
}
}
}
```

Hope this helps,

Michael