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 s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P I N
A L S I G
Y A H R
P I

Example 3:

Input: s = "A", numRows = 1
Output: "A"

Constraints:

• 1 <= s.length <= 1000
• s consists of English letters (lower-case and upper-case), ',' and '.'.
• 1 <= numRows <= 1000

SOLUTION:

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        n = len(s)
        if numRows == 1:
            return s
        op = ""
        for i in range(numRows):
            curr = i
            down = True
            while curr < n:
                op += s[curr]
                if down:
                    if numRows - i - 1 > 0:
                        curr += 2 * (numRows - i - 1)
                    else:
                        curr += 2 * i
                else:
                    if i > 0:
                        curr += 2 * i
                    else:
                        curr += 2 * (numRows - i - 1)
                down = not down
        return op