254. Factor Combinations

Topic:

Numbers can 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 are sorted ascending, for example:the factors of 2 and 6 [2, 6] are, not [6, 2] .
2. You are assume that n are always positive.
3. Factors should is greater than 1 and less than n.

Examples:
Input1
Output

[]

Input 37
Output

[]

Input 12
Output

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

Input 32
Output

[  2, +],  [2, 2, 8], [  2, 2, 2, 4],  [2, 2, 2, 2, 2],  [2, 4, 4], [4  , 8]]

Links: http://leetcode.com/problems/factor-combinations/

Exercises

Ask for a number of all factor, here we think of the DFS + backtracking, it should be noted that factor are >= 2, and in this problem, the number itself can not be counted as factor, so we have when n <= 1 o'clock judgment if ( List.size () > 1) Add the result to Res.

Time Complexity-o (2n), Space complexity-o (n).

 Public classSolution { PublicList<list<integer>> Getfactors (intN) {List<List<Integer>> res =NewArraylist<>(); List<Integer> list =NewArraylist<>(); Getfactors (res, list, N,2); returnRes; }        Private voidGetfactors (list<list<integer>> res, list<integer> List,intNintfactor) {        if(N <= 1) {            if(List.size () > 1) Res.add (NewArraylist<integer>(list)); return; }                 for(inti = factor; I <= N; i++) {            if(n% i = = 0) {list.add (i); Getfactors (res, list, n/I, i); List.remove (List.size ()-1); }        }    }}

Reference:

254. Factor Combinations