Combinations leetcode

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

Example

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 ArrayList<ArrayList<Integer>> combine(int n, int k) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> tem = new ArrayList<Integer>();
        if (n == 0 || k > n){
            return result;
        }
        dfs(result, tem, n, k, 1);
        return result;
    }
    public void dfs(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> tem, int n, int k, int pos){
        if (tem.size() == k){
            result.add(new ArrayList<Integer>(tem));
            return;
        }
        for(int i = pos; i <= n; i++){
            tem.add(i);
            dfs(result, tem, n, k, i+1);
            tem.remove(tem.size() - 1);
            }
        
    }
}