(java)leetcode-89:Gray Code

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.

解题思路：

这个题倒是没啥好说的，找到对应的规律就好了。

在n == 1的时候，序列为 0 1，其中1 = 1+0；

在n == 2的时候，序列为 0 1 3 2，其中3 = 2+1 , 2 = 2+0；

在n == 3的时候，序列为 0 1 3 2 6 7 5 4，其中6 = 4+2 , 7 = 4+3 , 5 = 4+1 , 4 = 4+0 ； 依次类推。

class Solution { public List<Integer> grayCode(int n) { List<Integer> result = new ArrayList(); result.add(0); int num = 1; for(int x = 0;x<n;x++) { int length = result.size(); for(int i = length-1;i>=0;i--) result.add(result.get(i)+num); num*=2; } return result; } }