[LeetCode]Factor Combinations

public class Solution {
    List<List<Integer>> result = new ArrayList<List<Integer>>();
    public List<List<Integer>> getFactors(int n) {
        if (n == 1) {
            return result;
        }
        helper(n, new ArrayList<Integer>(), 2);
        return result;
    }
    public void helper(int n, List<Integer> list, int pre) {
        if (n == 1) {
            if (list.size() > 1)
                result.add(list);
            return;
        }
        for (int i = pre; i <= n; i++) {
            if (n % i == 0) {
                List<Integer> l = new ArrayList<Integer>(list);
                l.add(i);
                helper(n / i, l, i);
            }
        }
    }
}