LeetCode "Combinations"

Typical recurrsionDFS problem. Just take care of memory use.

class Solution {
public:
    vector<vector<int>> ret;
    void go(int currMaxN, int currK, int k, unordered_set<int> set, vector<int> currRet)
    {
        if (currK == k)
        {
            ret.push_back(currRet);
            return;
        }

        auto it = set.begin();
        for (int i : set)
        {
            if (i > currMaxN)
            {
                vector<int> thisRet = currRet;
                thisRet.push_back(i);
                unordered_set<int> thisSet = set;
                thisSet.erase(i);
                go(i, currK + 1, k, thisSet, thisRet);
            }
        }
    }
    vector<vector<int> > combine(int n, int k) {
        if (k > 0)
        {
            unordered_set<int> set;
            for (int i = 1; i <= n; i++) set.insert(i);

            for (int i = 1; i <= n - k + 1; i++)
            {
                unordered_set<int> currSet = set;
                currSet.erase(i);
                vector<int> v; v.push_back(i);
                go(i, 1, k, currSet, v);
            }
        }
        return ret;
    }
};