[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.

class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> origin({0});
        for(int i=1;i<=n;i++)
        {
            int size = origin.size();
            int f = 1<<(i-1);
            for(int k=size-1;k>=0;k--)
            {
                origin.push_back(origin[k]|f);
            }
        }
        return origin;
    }
};