[LeetCode]Combinations

Backtrack的题目，没有什么好说的。时间复杂度O(C(n , k))，空间复杂度k，代码如下：

	class Solution {
	public:
	vector<vector<int>> combine(int n, int k) {
	if(k > n)return {};
	vector<vector<int>> res;
	vector<int> curr;
	backtrack(res, curr, 1, n, k);
	return res;
	}
	private:
	void backtrack(vector<vector<int>>& res, vector<int>& curr, int i, int n, int k)
	{
	if(curr.size() == k)
	{
	res.push_back(curr);
	return;
	}
	for(int j = i; j <= n; ++j)
	{
	curr.push_back(j);
	backtrack(res, curr, j+ 1, n, k);
	curr.pop_back();
	}
	}
	};

view raw Combinations.cpp hosted with ❤ by GitHub