Gray Code （格雷码编码） 【leetcode】

题目：

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 - 001 - 111 - 310 - 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.

看到坑爹的特判表示放弃，查了一下格雷码的生成，果然知识就是力量。

二进制转格雷码：

只要异或乘以二分之三，即二进制的1.1，然后忽略小数部分；也可以理解成异或乘以三（即11），再右移一位。

格雷码转二进制：

异或乘以三分之二，即除以1.1，忽略余数；或者左移一位，再异或除以三，忽略余数。

class Solution{public:vector<int> grayCode(int n){vector<int> ret;int maxx = 1 << n;for(int i = 0; i < maxx; ++i)ret.push_back((i >> 1)^i);return ret;}};