Leetcode Gray Code

The gray code is a binary numeral system where the successive values are 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:

00-001-111-310-2

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

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

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

Take 3-bit gray code as an example.
0 0 0
0 0 1
0 1 1
0 1 0
1 1 0
1 1 1
1 0 1
1 0 0
You can see that the nth bit of gray code consists of two parts, part of the n-1, plus the reverse of 1<< (n-1) and n-1 bit gray code

Class Solution {public:    vector<int> graycode (int n) {        if (n==0)        {            vector<int>ret;            Ret.push_back (0);            return ret;        }        else        {            vector<int>tmp=graycode (n-1);            vector<int>ret;            for (int i=0;i<tmp.size (); ++i)            {                ret.push_back (tmp[i]);            }            for (int i=tmp.size () -1;i>=0;--i)            {                Ret.push_back ((1<< (n-1)) +tmp[i]);            }            return ret;}}    ;

Leetcode Gray Code