LeetCode – Factor Combinations (Java)

 

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.

Java Solution

public List<List<Integer>> getFactors(int n) {
    List<List<Integer>> result = new ArrayList<List<Integer>>();
    List<Integer> list = new ArrayList<Integer>();
    helper(2, 1, n, result, list);
    return result;
}
 
public void helper(int start, int product, int n, List<List<Integer>> result, List<Integer> curr){
    if(start>n || product > n )
        return ;
 
    if(product==n) {
        ArrayList<Integer> t = new ArrayList<Integer>(curr);
        result.add(t);
        return;
    }   
 
    for(int i=start; i<n; i++){
        if(i*product>n)
            break;
 
        if(n%i==0){
            curr.add(i);
            helper(i, i*product, n, result, curr);
            curr.remove(curr.size()-1);
        }
    }
}

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  3. LeetCode – Unique Binary Search Trees II (Java)
  4. LeetCode – Combinations (Java)
Category >> Algorithms  
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  1. Int64 on 2017-5-27

    only n/2 iterations should be needed in for loop `for(int i=start; i<n; i++)`

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