vector<int> result;

/*

void genDigit(int& code, int n, int m) {

int len = 1 << (m + 2);

n &= ((1 << (m + 2)) - 1);

if (n >= (len >> 2) && n < len - (len >> 2)) {

code |= 1 << m;

}

else {

code &= ~(1 << m);

}

}

vector<int> grayCode(int n) {

int round = 1 << n;

int code;

result.clear();

for (int i = 0; i < round; i++) {

code = 0;

for (int j = 0; j < n; j++) {

genDigit(code, i, j);

}

result.push_back(code);

}

return result;

}