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FactorCombinations.java
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FactorCombinations.java
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/*
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:
You may assume that n is always positive.
Factors should be greater than 1 and less than n.
Example 1:
Input: 1
Output: []
Example 2:
Input: 37
Output:[]
Example 3:
Input: 12
Output:
[
[2, 6],
[2, 2, 3],
[3, 4]
]
Example 4:
Input: 32
Output:
[
[2, 16],
[2, 2, 8],
[2, 2, 2, 4],
[2, 2, 2, 2, 2],
[2, 4, 4],
[4, 8]
]
Analysis: Classic DFS problem, similar to Combination.
*/
class Solution {
public List<List<Integer>> getFactors(int n) {
List<List<Integer>> results = new ArrayList<>();
helper(results, new ArrayList<Integer>(), n, 2);
return results;
}
void helper(List<List<Integer>> results, List<Integer> list, int n, int factor){
if(n <= 1){
if(list.size() > 1){
results.add(new ArrayList<Integer>(list));
}
return;
}
for(int i = factor; i <= n; i++){
if(n % i == 0){
list.add(i);
helper(results, list, n/i, i);
list.remove(list.size() - 1);
}
}
}
}