89. Gray Code (Bit)

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.

思路：

二进制-->格雷码：如果二进制码字的第i位和i+1位相同，则对应的格雷码的第i位为0，否则为1。最高为之前可以看作还有一位0，即最高位是和0异或。

*格雷码-->二进制：最左边一位不变，从左边第二位起，将每位与左边一位解码后的值异或，作为该位解码后的值。

class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> result;
        int size = 1 << n;
        for (int i =0; i< size; i++)
        {
            result.push_back(getGrayCode(i));
        }
        return result;
    }
    int getGrayCode(int binary)
    {
        return ((binary >> 1)^binary);
    }
};