class Solution {
public:
    string convert(string s, int numRows) {
        int size = s.size(), diagon = numRows - 2, t, tr;
        if (!size || numRows < 2 || numRows >= size)
            return s;
        string ans;
        for (int i = 0; i < numRows; ++i)
        {
            t = i;
            while (t < size)
            {
                ans.push_back(s[t]);
                tr = (numRows - 1 - i) * 2;
                if (i != 0 && i != numRows - 1 && t + tr < size)
                {
                    ans.push_back(s[t + tr]);
                }
                t += numRows + diagon;
            }
        }
        return ans;
    }
};