题目链接

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.                                                                                    本文地址

分析：关于格雷码请参考wiki 和 百度百科。

二进制转格雷码：gray = (binary) xor (binary >> 1)

代码如下：

 class Solution {

 public:

     vector<int> grayCode(int n) {

         //注意n = 0时，输出{0}而不是空数组

         int num = <<n;

         vector<int> res;

         res.reserve(num);

         for(int i = ; i < num; i++)

             res.push_back(i^(i>>));

         return res;

     }

 };

这篇文章有一个对格雷码很有意思的解释

顺便科普一下解码（格雷码 转 二进制码）方法（摘自百度百科）：

公式表示：

（G：格雷码，B：二进制码）

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