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. http://leetcode.com/onlinejudge

leetcode_gray_code.cpp

class Solution {
public:
    vector<int> grayCode(int n) {
        vector<int> ret;
        if (n == 0) {
            ret.push_back(0);
            return ret;
        }
        else if (n == 1) {
            ret.push_back(0);
            ret.push_back(1);
            return ret;
        }
        else {
            vector<int> tmp = grayCode(n - 1);
            ret = tmp;
            for (int i = tmp.size() - 1; i >= 0; --i)
                ret.push_back(tmp[i] + ( 1 << (n - 1)));
            return ret;
        }
    }
};