Add to List 77. Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.
For example,

If n = 4 and k = 2, a solution is:

[
[2,4],
[3,4],
[2,3],
[1,2],
[1,3],
[1,4],
]

public class Solution {
public List<List<Integer>> combine(int n, int k) {
List<List<Integer>> data = new ArrayList<>();
if (n == 0 || n < k)
return data;
helper(data, new LinkedList<Integer>(), n, k);
return data;
}
public void helper(List<List<Integer>> data, List<Integer> temp, int n, int k) {
for (int i = n; i >= k; --i) {
if (k == 0) {
data.add(temp);
break;
} else {
LinkedList<Integer> next = new LinkedList<>(temp);
next.addFirst(i);
helper(data, next, i - 1, k - 1);
}
}
}
}