LeetCode 6. Zigzag transformation (n-shaped transformation)

Will a given string s According to the given number of rows numRows , From top to bottom 、 Left to right Z Font arrangement .

For example, the input string is “PAYPALISHIRING” The number of rows is 3 when , Arranged as follows ：

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

after , Your output needs to be read line by line from left to right , Generate a new string , such as ：“PAHNAPLSIIGYIR”.

Please implement this function to transform a string into a specified number of lines ：

string convert(string s, int numRows);

Example 1：

Input ：s = “PAYPALISHIRING”, numRows = 3
Output ：“PAHNAPLSIIGYIR”
Example 2：
Input ：s = “PAYPALISHIRING”, numRows = 4
Output ：“PINALSIGYAHRPI”
explain ：
P I N
A L S I G
Y A H R
P I
Example 3：

Input ：s = “A”, numRows = 1
Output ：“A”

//  This question should be N  Glyph conversion 
class Solution {
    
public:
    string convert(string s, int numRows) {
    
        string re;
        if(numRows == 1) return s;
        //  Looking for a regular 
        for(int j =0; j < numRows; j++)
        {
    
            if(j == 0 || j == numRows -1 )
            {
    
                for(int i = j; i<s.size(); i += 2 * numRows - 2)
                    re += s[i];
            }
            else
            {
    
                for(int i = j, k = 2 * numRows -2 - j; i < s.size() || k < s.size() ;i += 2 * numRows -2, k += 2 * numRows -2)
                {
    
                    if(i < s.size()) re += s[i];   //  Add the front one first 
                    if(k < s.size()) re += s[k];
                }
            }
        }
        return re;
    }
};