Combination question of leetcode

Combination.java

public class Solution {
    public ArrayList<ArrayList<Integer>> combine(int n, int k) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if(n <= 0 || k<=0)
            return result;
        ArrayList<Integer> temp = new ArrayList<Integer>();
        
        dfsWorker(n, k, result, temp, 1);
        return result;
    }
    
    public void dfsWorker(int n, int k, ArrayList<ArrayList<Integer>> result, ArrayList<Integer> temp, int currentPosition){
        for(int i = currentPosition;i<=n;i++){
            temp.add(i);
            if(temp.size() == k)
                result.add(new ArrayList<Integer>(temp));
            else    
                dfsWorker(n, k, result, temp, i+1);
            
            //remove the elements from temp before return
            temp.remove(temp.size()-1);
        }
    }
}