[LeetCode 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]
]

Diffculty
Medium

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Analysis