gray_code.cpp

/*
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) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<int> res;
        res.push_back(0);

        if (n == 0) return res;
        res.push_back(1);

        int add = 1;
        for (int i = 1; i < n; i++) {
            add *= 2;
            for (int j = res.size() - 1; j >= 0; j--)
                res.push_back(res[j] + add);
        }

        return res;
    }
};