static string convert(string s, int numRows) {
        string result;
        int length = 2 * numRows - 2;
        string save[numRows];
        for (int i = 0; i < numRows; i++)
            for (int j = i; j < s.length(); j += length) {
                save[i] += s[j];
                if (i != 0 && i != numRows - 1 && j + length - 2 * i < s.length())
                    save[i] += s[j + length - 2 * i];
            }
        for (int i = 0; i < numRows; i++)
            result += save[i];
        return result;
    }