0006-ZigZag-Conversion.py

'''
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
'''
class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows == 1:
            return s
        
        res = ''
        n = len(s)
        cycle_len = 2 * numRows - 2
        
        for i in range(numRows):
            j = 0
            while j + i < n:
                res += s[j + i]
                if i != 0 and i != numRows - 1 and j + cycle_len - i < n:
                    res += s[j + cycle_len - i]
                j += cycle_len
        return res