[LeetCode]Combinations

class Solution {//using recurrence to get these combinationspublic:vector<vector<int> > combine(int n, int k) {// Start typing your C/C++ solution below// DO NOT write int main() functionvector<int> temp;vector<vector<int> > ans;combine_rec(ans , temp , n , k , 1);return ans;}void combine_rec(vector<vector<int> > &ans , vector<int>& temp , int n , int k , int index) {if (k == 0)ans.push_back(temp);else if (k > 0 && index <= n){temp.push_back(index);combine_rec(ans , temp , n , k-1 , index+1);temp.pop_back();combine_rec(ans , temp , n , k , index+1);}}};

second time

class Solution {public:    void combineUtil(int n, int k, int curIdx, vector<int>& curPath, vector<vector<int> >& allPath)    {        if(curPath.size() == k)         {            allPath.push_back(curPath);            return;        }        if(curIdx >= n+1) return;                combineUtil(n, k, curIdx+1, curPath, allPath);        curPath.push_back(curIdx);        combineUtil(n, k, curIdx+1, curPath, allPath);        curPath.pop_back();    }    vector<vector<int> > combine(int n, int k) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector<int> curPath;        vector<vector<int> > allPath;        combineUtil(n, k, 1, curPath, allPath);         return allPath;    }};