leetcode 77. Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,
If n = 4 and k = 2, a solution is:

[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

class Solution {
	void choose_one(vector<pair<vector<int>, vector<int>>>&candi)
	{
		vector<pair<vector<int>, vector<int>>>newcandi;
		for (int i = 0; i < candi.size(); i++)
		{
			for (int j = 0; j < candi[i].second.size(); j++)
			{
				vector<int>bb = candi[i].first;
				bb.push_back(candi[i].second[j]);
				vector<int>cc = candi[i].second;
				cc.erase(cc.begin(), cc.begin() + j + 1);
				newcandi.push_back(pair<vector<int>, vector<int>>(bb, cc));
			}
		}
		candi = newcandi;
	}
public:
	vector<vector<int>> combine(int n, int k) {
		vector<vector<int>>re;
		vector<int>aa;
		if (k == 0)
		{
			re.push_back(aa);
			return re;
		}
		vector<int>nums;
		for (int i = 0; i < n; i++)
			nums.push_back(i + 1);
		vector<pair<vector<int>, vector<int>>>candi;
		candi.push_back(pair<vector<int>, vector<int>>(aa, nums));
		int kk = 0;
		while (kk < k)
		{
			choose_one(candi);
			kk++;
		}
		for (int i = 0; i < candi.size(); i++)
			re.push_back(candi[i].first);
		return re;
	}
};

accepted