[leetcode.com]算法题目 - 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.

根据题目中的意思，我们只要求出一组合适的解即可。正确答案非常精妙（我没有想出来。。。），充分利用位运算。看来对于位运算的知识我还是要再加强。

答案出处：http://www.2cto.com/kf/201305/215316.html

 1 class Solution {

 2 public:

 3     

 4     vector<int> grayCode(int n) {

 5         // Start typing your C/C++ solution below

 6         // DO NOT write int main() function

 7         vector<int> result;

 8         int m=1<<n;

 9         for(int i=0;i<m;i++)

10         {

11             result.push_back(i^(i>>1));

12         }

13         return result;

14         

15     }

16 };

参考答案

思路：首先，1<<n 是用来计算2的n次方。i^(i>>1)是格雷码的计算方法，表示第i个数是几。好久不用都想不起来了。。。