leetcode[89]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> res;
    if (n==0)
    {
        res.push_back(n);
        return res;
    }
    vector<int> tmp=grayCode(n-1);
    res.insert(res.end(),tmp.begin(),tmp.end());
    int base=1<<(n-1);
    for (int i=tmp.size()-1;i>=0;i--)
    {
        res.push_back(base+tmp[i]);
    }
    return res;
}
};