package leetcode_1To300;

import java.util.ArrayList;
import java.util.List;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
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 */
public class _254_FactorCombinations {

    /**
     * 254. Factor _77_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:
     You may assume that n is always positive.
     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]
     ]

     * @param n
     * @return
     */

    public List<List<Integer>> getFactors(int n) {
        List<List<Integer>> res = new ArrayList<>();
        helper(res, new ArrayList<>(), n, 2);
        return res;
    }
    public void helper(List<List<Integer>> res, List<Integer> list, int n, int start) {
        if (n == 1) {
            if (list.size() > 1) {
                res.add(new ArrayList<>(list));
                return;
            }
        }
        for (int i = start; i <= n; i++) {
            if (n % i == 0) {
                list.add(i);
                helper(res, list, n / i, i);
                list.remove(list.size() - 1);
            }
        }
    }
}