Factor Combinations leetcode

Numbers can be regarded as product of its factors. For example,

8 = 2 x 2 x 2;
  = 2 x 4.

Write a function that takes an integer n and return all possible combinations of its factors.

Note: 

1. Each combination's factors must be sorted ascending, for example: The factors of 2 and 6 is [2, 6], not [6, 2].
2. You may assume that n is always positive.
3. Factors should be greater than 1 and less than n.

Examples: 
input: 1
output: 

[]

input: 37
output: 

[]

input: 12
output:

[
  [2, 6],
  [2, 2, 3],
  [3, 4]
]

input: 32
output:

[
  [2, 16],
  [2, 2, 8],
  [2, 2, 2, 4],
  [2, 2, 2, 2, 2],
  [2, 4, 4],
  [4, 8]
]

用dfs方法,

public class Solution {
    public List<List<Integer>> getFactors(int n) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if (n <= 2) {
            return res;
        }
        List<Integer> tem = new ArrayList<Integer>();
        helper(res, tem,n,2);
        return res;
    }
    public void helper(List<List<Integer>> res, List<Integer> tem, int m,int div) {
        if (m <= 1) {
            if (tem.size() > 1) {
                res.add(new ArrayList<Integer>(tem));
            }
            return;
        }
        for (int i = div; i <= m; i++) {
            if (m % i == 0) {
                tem.add(i);
                helper(res, tem,m / i, i);
                tem.remove(tem.size() - 1);
            }
            
        }
    }
}