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.

Solution:

I have learned about gray code in class before ,but I totally forget about it. then use some small case to find the relationship between them. the job will be done.

class Solution {
public:
    vector<int> grayCode(int n) {
        // Start typing your C/C++ solution below
		// DO NOT write int main() function
		vector<int> res;
        if(n ==0){
            res.push_back(0);
            return res;
        }
		else{
			res = grayCode(n-1);
			int pos = (1<<(n-1)) - 1;
			int cur = 1 + pos;
			for(int i = pos; i >= 0; --i){
				res.push_back(cur | res[i]);
			}
			return res;
		}
	}
};