89. Gray Code java solutions

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.

public class Solution {
    public List<Integer> grayCode(int n) {
        List<Integer> ans = new ArrayList<Integer>();
        int len = (int)Math.pow(2,n);
        for(int i = 0; i< len ;i++){
            ans.add(i^(i>>1));// 按照数学公式的解法。G(N) = (B(n)/2) XOR B(n).
        }
        return ans;
    }
}

二进制数转格雷码

（假设以二进制为0的值做为格雷码的0）

G：格雷码 B：二进制码

G(N) = (B(n)/2) XOR B(n).

以三位为例:

000^000-->000

001^000-->001

010^001-->011

011^001-->010

100^010-->110

101^010-->111

110^011-->101

111^011-->100

解法二： 可用递归。以后在总结。

参考帖子：

http://blog.csdn.net/makuiyu/article/details/44926463

http://www.cnblogs.com/peihao/p/5269151.html （第二个帖子描述的还是不够清晰一些）