254. Factor Combinations 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: Each combination''s factors must be sorted ascending, for example: The factors of 2 and 6 is [2, 6], not [6, 2]. You may assume that n is always positive. 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] ] public List> getFactors(int n) { List> result = new ArrayList>(); helper(result, new ArrayList(), n, 2); return result; } public void helper(List> result, List item, int n, int start){ if (n <= 1) { if (item.size() > 1) { result.add(new ArrayList(item)); } return; } for (int i = start; i <= Math.sqrt(n); ++i) { if (n % i == 0) { item.add(i); helper(result, item, n/i, i); item.remove(item.size()-1); } } }