Leetcode: Combination in C++

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],
]

Solution: 
void helper(vector<vector<int> >& result,vector<int> current, int k, int n, int cur )
    {
        if(current.size()==k)
        {
            result.push_back(current);
            return;
        }
        for(int i=cur;i<=n;i++)
        {
            current.push_back(i);
            helper(result,current,k,n,i+1);
            current.pop_back();
        }
    }
    vector<vector<int> > combine(int n, int k) {
        vector<vector<int> > result;
        vector<int> solution;  
        helper(result,solution, k,n,1);
        return result;
    }