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 {
public:
void helper(vector<vector<int> > &svec, vector<int> &vec, int start, int n, int k)
{
if(vec.size() == k)
{
svec.push_back(vec);
return;
}
for(int i = start; i < n; ++ i)
{
vec.push_back(i + 1);
helper(svec, vec, i + 1, n, k);
vec.pop_back();
}

}
vector<vector<int> > combine(int n, int k)
{
vector<vector<int> > svec;
vector<int> vec;
if(n == 0 || k == 0)
{
return svec;
}
helper(svec, vec, 0, n, k);
return svec;
}
};