LeetCodeP89 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.

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.

题目大意：给定一个正整数代表二进制数的位数，求该位数的一个格雷码序列。

思路：只需要模拟格雷码的生成规则：

当位数为n时的格雷码可分为两部分：第一部分是位数为n-1时的格雷码；第二部分是位数为n-1时的格雷码倒叙并在每个最高位加1。

例如：

设n=0时，格雷码为0

n=1时

0    0

1    1

n=2时

00    0

01    1

11    3

10    2

以此类推。

代码：

public class Solution { public List<Integer> grayCode(int n) { List<Integer> result = new ArrayList<>(); result.add(0); for (int i = 0; i < n; i++) { int x = 1 << i; for (int j = result.size() - 1; j >= 0; j--) { result.add(x+result.get(j)); } } return result; } }