LeetCode 254. Factor Combinations

最新推荐文章于 2021-01-20 08:31:31 发布

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本文介绍了一种用于找出整数所有可能的因数组合的算法。该算法递归地寻找每个有效因数，并确保结果中因数序列的升序排列。通过具体实例展示了如何使用此算法来获取输入整数的有效因数分解。

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Almost the same idea as combinations (permutations)

#include <vector>
#include <iostream>
using namespace std;

/*
  Numbers can be regarded as product of its factor. 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 factor.
  Note:
  1: Each combination's factors must be sorted ascending, for example
     The factors of 2 and 6 is [2, 6], not [6, 2]
  2: You may assume that n is always positive.
  3: Factors should be greater than 1 and less than n.
  
  Example:
  Input: 37, Output: []
  Input: 12, Output: [[2, 6], [2, 2, 3], [3, 4]]
*/
void getFactors(int n, vector<int>& path, vector< vector<int> >& res, int start) {
  if(n == 1 && path.size() > 1) {
    res.push_back(path);
    return;
  }
  for(int i = start; i <= n; ++i) {
    if(n % i == 0) {
      path.push_back(i);
      getFactors(n / i, path, res, i);
      path.pop_back();
    }
  }
}
vector< vector<int> > getFactors(int n) {
  if(n <= 1) return {};
  vector<int> path;
  vector< vector<int> > res;
  getFactors(n, path, res, 2);
  return res;
}

int main(void) {
  vector< vector<int> > res = getFactors(8);
  for(int i = 0; i < res.size(); ++i) {
    for(int j = 0; j < res[i].size(); ++j) {
      cout << res[i][j] << " ";
    }
    cout << endl;
  }
}