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FactorCombination.java
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FactorCombination.java
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import java.util.ArrayList;
import java.util.List;
public class FactorCombination {
/**
*
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]
]
*/
public List<List<Integer>> getFactors(int n) {
List<List<Integer>> res = new ArrayList<>();
helper(res, new ArrayList<>(), n, 2);
return res;
}
private void helper(List<List<Integer>> res, List<Integer> list, int n, int start) {
if(n == 1) return;
if(list.size() >= 1) {
list.add(n);
res.add(new ArrayList<>(list));
list.remove(list.size() - 1);
}
for(int i = start; i <= n / 2; i++) {
if(n%i == 0) {
if(n / i >= i) {
list.add(i);
helper(res, list, n / i, i);
list.remove(list.size() - 1);
}
}
}
}
public static void main(String[] args) {
FactorCombination a = new FactorCombination();
a.getFactors(12);
}
}