# 254 Factor Combinations

## 1. Question

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 integernand return all possible combinations of its factors.

Note:

1. You may assume that n is always positive.

2. 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]
]``````

## 2. Implementation

(1) Backtracking

``````class Solution {
public List<List<Integer>> getFactors(int n) {
List<List<Integer>> res = new ArrayList<>();
List<Integer> factors = new ArrayList<>();
recGetFactors(2, n, factors, res);
return res;
}

public void recGetFactors(int factor, int curNum, List<Integer> factors, List<List<Integer>> res) {
if (curNum == 1 && factors.size() > 1) {
return;
}

for (int i = factor; i <= curNum; i++) {
if (curNum % i == 0)  {