vector<int> grayCode(int n) { vector<int> res; res.push_back(0); if (n == 0) return res; res.push_back(1); int total = 1 << n; for (int i = 2;i < total; i+=2) { int j = 1; while((res.back() & j) == 0) j <<= 1; j <<= 1; res.push_back(res.back() ^ j); res.push_back(res.back() ^ 1); } return res; }

vector<int> grayCode(int n) { vector<int> res; if (n == 0) { res.push_back(0); return res; } res.push_back(0); res.push_back(1); for (int i = 2; i <= n; i++) { int s = 1 << (i-1); for (int j = res.size() - 1; j >= 0; j--) { res.push_back(res[j] + s); } } return res; }