Z字形变换

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows < 2: return s
        res = ["" for _ in range(numRows)]
        i, flag = 0, -1
        for c in s:
            res[i] += c
            if i == 0 or i == numRows - 1: flag = -flag
            i += flag
        return "".join(res)

作者：jyd
链接：https://leetcode-cn.com/problems/zigzag-conversion/solution/zzi-xing-bian-huan-by-jyd/
来源：力扣（LeetCode）
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