Combination Sum III

挺简单的一道题，也出了3个错误，如何bug free啊

public class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> result = new LinkedList<>();
if (k == 0 || n < 1) {
return result;
}
List<Integer> list = new LinkedList<>();
//1 combinationSum3Helper(result, list, k, n, 0);
combinationSum3Helper(result, list, k, n, 1);
return result;
}

private void combinationSum3Helper(List<List<Integer>> result, List<Integer> list, int k, int n, int pos) {
if (k == 0 && n == 0) {
result.add(new LinkedList<>(list));
return;
} else if (n < 0 || k < 0) {
return;
}
//2 for (int i = pos; i <= n; i++) {
for (int i = pos; i <= 9; i++) {
list.add(i);
//3 ombinationSum3Helper(result, list, k - 1, n - i, i++);
combinationSum3Helper(result, list, k - 1, n - i, i + 1);
list.remove(list.size() - 1);
}

}
}

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]]