ZigZag Conversion

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

class Solution {
public:
    string convert(string s, int nRows) {
        if (nRows == 1 || nRows >= s.size()) 
        {
            return s;
        }
        
        string str;
        int edge = nRows - 1;
        for (int i = 0; i < nRows; ++i) 
        {
            int k = i;
            while (k < s.size()) 
            {
                str += s[k];
                if (i == 0 || i == edge) 
                {
                    k += 2 * edge;
                }
                else
                {
                    k += 2 * (edge - k % (edge));
                }
            }
        }
        return str;
    }
};