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.

class Solution 
{
public:
    vector<int> grayCode(int n) 
    {
        vector<int> bin(n,0);
        vector<int> res;
        if(n==0)
        {
            res.push_back(0);
            return res;
        }
        int hold = 1;
        for(int i=0; i<n; i++)
            hold = hold*2;
        for(int i=0; i<hold;i++)
        {
            vector<int> gray(n,0);
            gray[0] = bin[0];
            int x = hold/2;
            int temp = gray[0]*x;
            x = x/2;
            for(int j=1; j<n; j++)
            {
                gray[j] = bin[j-1] ^ bin[j];
                temp = temp + x*gray[j];
                x = x/2;
            }
            res.push_back(temp);
            int count = 0;
            temp = 1;
            for(int j=n-1; j>=0; j--)
            {
                count = bin[j] + temp + count;
                bin[j] = count%2;
                count = count/2;
                temp = 0;
            }
        }
        return res;
    }
};

LeetCode--Gray Code