题目描述：

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

解题思路：第i个graycode为(i>>1)^i。

代码：

vector<int> Solution::grayCode(int n)
{
    vector<int> ans;
    int num = 1 << n;
    for(int i = 0;i < num;i++)
        ans.push_back((i>>1)^i);
    return ans;
}

LeetCode：GrayCode