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".

Runtime: 16ms

class Solution {
public:
    string convert(string s, int numRows) {
        if(numRows <= 1) return s;
        if(s.empty()) return s;
        
        string result;
        int size = 2 * numRows - 2;
        for(int i = 0; i < numRows; i++){
            for(int j = i; j < s.length(); j += size){
                result += s[j];
                if(i != 0 && i != numRows - 1){
                    int temp = j + size - 2 * i;
                    if(temp < s.length())
                        result += s[temp];
                }
            }
        }
        return result;
    }
};