[LeetCode]Gray Code

题目描述：(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.

解题思路：

该题目要求给出所有n比特格雷码序列，整数n的格雷码的数学公式：n ^ (n / 2)。

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