[Swift]LeetCode254.因子组合 $ 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:

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]
]

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

编写一个接受整数n并返回所有可能的因子组合的函数。

注：

每个组合的因子必须按升序排序，例如：2和6的因子是[2，6]，而不是[6，2]。

你可以假设n总是正的。

系数应大于1且小于n。

实例：

输入：1

输出：

[]

输入：37

输出：

[]

输入：12

输出：

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

输入：32

输出：

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

 1 class Solution {
 2     func getFactors(_ n:Int) -> [[Int]]{
 3         var res:[[Int]] = [[Int]]()
 4         var arr:[Int] = [Int]()
 5         helper(n,2,&arr,&res)
 6         return res
 7     }
 8
 9     func helper(_ n:Int,_ start:Int,_ out:inout [Int],_ res:inout [[Int]])
10     {
11         var num:Int = Int(floor(sqrt(Double(n))))
12         var i :Int = start
13         while(i <= num)
14         {
15             if n % i == 0
16             {
17                 var new_out:[Int] = out
18                 new_out.append(i)
19                 helper(n / i, i, &new_out, &res)
20                 new_out.append(n / i)
21                 res.append(new_out)
22             }
23             i += 1
24         }
25     }
26 }

原文地址：https://www.cnblogs.com/strengthen/p/10225203.html