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) {
        std::vector<int> result;
            result.push_back(0);
            for (int i = 0; i < n; ++i)
            {
                int adder = 1 << i;
                int len = result.size();
                for (int i = len -1 ; i >= 0; --i)
                {
                    int element = result[i] + adder;
                    result.push_back(element);
                }
            }
        return result;
    }
};