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class Solution {//using recurrence to get these combinationspublic:	vector
   
    
      > combine(int n, int k) {		// Start typing your C/C++ solution below		// DO NOT write int main() function		vector
     
       temp;		vector
      
       
         > ans;		combine_rec(ans , temp , n , k , 1);		return ans;	}	void combine_rec(vector
        
         
           > &ans , vector
          
           & 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
   
    & curPath, vector
    
     
       >& 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
      
       
         > combine(int n, int k) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        vector
        
          curPath; vector
         
          
            > allPath; combineUtil(n, k, 1, curPath, allPath); return allPath; }};
          
         
        
       
      
     
    
   

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