Gray Code

 1     //reference http://blog.csdn.net/fightforyourdream/article/details/14517973
 2     vector<int> grayCode(int n) {
 3         vector<int> codes;
 4         if(n<0)
 5             return codes;
 6         int size=1<<n;//相当于2的n次方
 7         int i,tmp;
 8         for(i=0;i<size;++i)
 9         {
10             tmp=i^i>>1;
11             codes.push_back(tmp);
12         }
13         return codes;
14     }