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(object):
    def convert(self, s, numRows):
        if numRows == 1:
            return s 
        n = len(s)
        cycle = 2*numRows - 2
        strlist = []
        for i in range(numRows):
            for j in range(i, n, cycle):
                strlist.append(s[j])
                if i != numRows-1 and i != 0 and j+cycle-2*i < n:
                    strlist.append(s[j+cycle-2*i])             
        newstr = ''.join(strlist)
        return newstr