示例2中共产生4行数据，定义 index 变量，用于控制每次取数之后应该放到哪一行。
0 0 0
1 1 1 1 1
2 2 2 2 2
3 3 3
class Solution: def convert(self, s: str, numRows: int) -> str: if numRows == 1: return s result = ['' for _ in range(numRows)] i = 0 # numRows index for v in s: result[i] += v if i == 0: tag = 1 if i == numRows - 1: tag = -1 i += tag return "".join(result)
