Description：

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

计算格雷码的十进制数。套用格雷码编码公式解决。

public class Solution {

    public List<Integer> grayCode(int n) {

        List<Integer> res = new ArrayList<Integer>();

        for(int i=0; i<(1<<n); i++)

            res.add(i/2 ^ i);

        return res;

    }

}