class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows == 1:
            return s

        res = []
        for r in range(numRows):
            increment = 2 * (numRows - 1)
            for i in range(r, len(s), increment):
                res.append(s[i])
                if r > 0 and r < numRows - 1 and i + increment - 2 * r < len(s):
                    res.append(s[i + increment - 2 * r])

        return ''.join(res)

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows == 1 or numRows >= len(s):
            return s

        res = [[] for _ in range(numRows)]
        row, dir = 0, 1
        for c in s:
            res[row].append(c)
            row += dir
            if row == 0 or row == (numRows - 1):
                dir *= -1

        return ''.join([''.join(row) for row in res])