Combinations

class Solution
{
public:
    vector<vector<int>> combine(int n, int k)
    {
        vector<int> one;
        for (int i = n - k + 1; i <= n; ++i)
        {
            one.push_back(i);
        }
        
        vector<vector<int>> all({one});
        while (true)
        {
            int i = k - 1;
            for (; i > 0; --i)
            {
                if (one[i] > one[i-1] + 1)
                {
                    break;
                }
            }
            
            if (i > 0 || one[i] > 1)
            {
                one[i] -= 1;
                for (int j = k - 1; j > i; --j)
                {
                    one[j] = n + 1 - k + j;
                }
            }
            else
            {
                break;
            }
            
            all.push_back(one);
        }
        
        return all;
    }
};