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6. Zigzag Conversion

https://leetcode.com/problems/zigzag-conversion/

Python

公式拿Excel觀察歸納出來的，有k欄(即題目的numRows)，該字元的index為i，則：

b = k - \mid i \bmod (k \cdot 2-2) - i + 1 \mid - 1

Time: O(N)
Space: O(N)

class Solution:
    def convert(self, s: str, numRows: int) -> str:
        if numRows < 2:
            return s

        mapper = [[] for i in range(numRows)]

        for i, char in enumerate(s):
            bucket = numRows - abs(i%(numRows*2-2)-numRows+1) - 1
            mapper[bucket].append(char)

        return ''.join([char for bucket in mapper for char in bucket])

Python