LeetCode Problem : Gray Code

Problem

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.

Code

vector<int> grayCode(int n) {
    // IMPORTANT: Please reset any member data you declared, as
    // the same Solution instance will be reused for each test case.
    if(n == 0)
        return vector<int>(1,0);
    vector<int> ret = grayCode(n - 1);
    vector<int> result;
    copy(ret.begin(),ret.end(),back_inserter<vector<int> >(result));
    vector<int>::const_reverse_iterator it = ret.rbegin();
    int one = (1 << (n - 1));
    for(;it != ret.rend();++it){
        result.push_back(one | *it);
    }
    return result;
}