[Leetcode] Gray Code

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:

00 - 0
01 - 1
11 - 3
10 - 2

Note:
For a given n, a gray code sequence is not uniquely defined.

For example, [0,2,3,1] is also a valid gray code sequence according to the above definition.

For now, the judge is able to judge based on one instance of gray code sequence. Sorry about that.

Analysis:

    vector<int> grayCode(int n) {
  
        vector<int> codes(1,0);
        for (int i = 0; i<n; i++)
        {
            for (int j=codes.size()-1; j >=0 ; j--)
            {
                int code = 0x1 << i | codes[j];
                codes.push_back(code);
            }
        }
        
        return codes;
    }