Gray Code -- LeetCode

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.

思路：利用位运算，将当前结果中的所有数最前面添上一个1，直到达到n位位置。时间复杂度O(n)

class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> res(1, 0);
        if (n == 0) return res;
        int offset = 1;
        for (int i = 0; i < n; i++)
        {
            for (int j = res.size() - 1; j >= 0; j--)
                res.push_back(res[j] | offset);
            offset = offset << 1;
        }
        return res;
    }
};