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.
思路：每次获取当前向量的长度，而该长度正好是当前格雷码的最高位，然后用该最高位去和向量中的数据进行异或，注意要从后向前，即到到下一组格雷吗
class Solution {
public:
vector<int> grayCode(int n) {
vector<int> res(1,0);
int i;
while(n--)
{
int highbit = res.size();//当前二进制的最高为1的位
for(i = res.size()-1;i >= 0;--i)res.push_back(highbit|res[i]);
}
return res;
}
};原文：http://blog.csdn.net/fangjian1204/article/details/38869967