Gray Code

 1 class Solution {
 2 public:
 3     vector<int> grayCode(int n) {
 4         vector<int> res;
 5         if(n==0)
 6         {
 7             res.push_back(0);
 8         }
 9         else if(n==1)
10         {
11             res.push_back(0);
12             res.push_back(1);
13         }
14         else
15         {
16             vector<int> res1=grayCode(n-1);
17             int size1=res1.size();
18             res.insert(res.begin(),res1.begin(),res1.end());
19     
20             
21             int addNumber=1<<(n-1);
22             for(int i=size1-1;i>=0;i--)
23             {
24                 res.push_back(addNumber+res.at(i));
25             }
26         }
27         return res;
28         
29         
30     }
31 };