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)
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 };