77. Combinations

77. Combinations

题目

 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],
]

解析

class Solution_77 {
public:

	void help(vector<vector<int>>& vecs, vector<int> &vec,int i,int k,int n )
	{
		if (k==0)
		{
			vecs.push_back(vec);
			return;
		}
		if (i>n)
		{
			return;
		}

		vec.push_back(i + 1);
		help(vecs, vec, i + 1, k-1, n);
		vec.pop_back();
		help(vecs, vec, i + 1, k, n);

		return;

	}

	vector<vector<int>> combine(int n, int k) {

		vector<vector<int>> vecs;
		vector<int> vec;

		help(vecs,vec,0,k,n);

		return vecs;  
	}
};

题目来源

• 77. Combinations