# 19.2.23 [LeetCode 89] Gray Code

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.

Example 1:

Input: 2
Output: [0,1,3,2]
Explanation:
00 - 0
01 - 1
11 - 3
10 - 2

For a given n, a gray code sequence may not be uniquely defined.
For example, [0,2,3,1] is also a valid gray code sequence.

00 - 0
10 - 2
11 - 3
01 - 1

Example 2:

Input: 0
Output: [0]
Explanation: We define the gray code sequence to begin with 0.
A gray code sequence of n has size = 2n, which for n = 0 the size is 20 = 1.
Therefore, for n = 0 the gray code sequence is [0].

## 题解

1 class Solution {
2 public:
3     vector<int> grayCode(int n) {
4         vector<int>ans;
5         if (n == 0) {
6             ans.push_back(0);
7             return ans;
8         }
9         ans = grayCode(n - 1);
10         int m = ans.size(), pls = (1 << (n - 1));
11         for (int i = m - 1; i >= 0; i--)
12             ans.push_back(pls + ans[i]);
13         return ans;
14     }
15 };
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posted @ 2019-02-23 13:50  TobicYAL  阅读(176)  评论(0编辑  收藏  举报