Combination Sum III leetcode

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.

Ensure that numbers within the set are sorted in ascending order.

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>> res = new ArrayList<List<Integer>>();
        if (k <= 0) {
            return res;
        }
        List<Integer> tem = new ArrayList<Integer>();
        helper(res, tem, k, n, 1, 0, 0);
        return res;
    }
    public void helper(List<List<Integer>> res, List<Integer> tem, int k, int n, int pos, int sum, int count) {
        if (sum == n && count == k) {
            res.add(new ArrayList<Integer>(tem));
            return;
        }

        for (int i = pos; i <= 9; i++) {
            tem.add(i);
            helper(res, tem, k, n, i + 1, sum + i, count+1);
            tem.remove(tem.size() - 1);
        }
    }
}