Gray Code -- LeetCode

Posted 2020-06-10

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)

 1 class Solution {
 2 public:
 3     vector<int> grayCode(int n) {
 4         vector<int> res(1, 0);
 5         if (n == 0) return res;
 6         int offset = 1;
 7         for (int i = 0; i < n; i++)
 8         {
 9             for (int j = res.size() - 1; j >= 0; j--)
10                 res.push_back(res[j] | offset);
11             offset = offset << 1;
12         }
13         return res;
14     }
15 };