Leetcode | 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 (s.empty() || nRows <= 1) return s;
        stringstream ss;
        int n = s.length();
        for (int row = 0; row < nRows; ++row) {
            for (int i = row; i < n; ) {
                if (nRows - row - 1 > 0) {
                    ss << s[i];
                    i += 2 * (nRows - row - 1);
                    if (i >= n) break;
                    
                }
                if (row > 0) {
                    ss << s[i];
                    i += 2 * row;
                    if (i >= n) break;
                }
            }
        }
        return ss.str();
    }
};