zigzag-conversion.py

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows == 1 or numRows > len(s):
            return s
        zigzag = ["" for i in range(numRows)]
        row, step = 0, 1
        for char in s:
            zigzag[row] += char
            if row == 0:
                step = 1
            elif row == numRows - 1:
                step = -1
            row += step
        return "".join(zigzag)