[leetcode.com]算法题目

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 - 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

class Solution {
public:
    
    vector<int> grayCode(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> result;
        int m=1<<n;
        for(int i=0;i<m;i++)
        {
            result.push_back(i^(i>>1));
        }
        return result;
        
    }
};

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。。。