/**The gray code is a binary numeral system where two successive values differ in only one bit.

*

*Given a non-negative integer n representing the total number of bits in the code, print the

* sequence of gray code. A gray code sequence must begin with 0.

*

*For example, given n = 2, return [0,1,3,2]. Its gray code sequence is:

**/

class Solution {

public:

vector<int> grayCode(int n) {

vector<int> res(1,0);

int i;

for(i = 0; i < n; i++)

{

int cur = res.size();

while(cur)

{

cur--;

int temp = (1<<i);

temp += res[cur];

res.push_back(temp);

}

}

return res;

}

};