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

ZigZag_Conversion_Leetcode.py

class Solution(object):
    def convert(self, s, numRows):
        if numRows == 1: return s
        arr_of_arr = [[] for i in range(numRows)]
        running_index, direction = 0, 1
        for c in s:
            arr_of_arr[running_index].append(c)
            running_index += direction
            if running_index>=numRows:
                running_index, direction = numRows-2, -1
            if running_index<0:
                running_index, direction = 1, 1
        return ''.join(sum(arr_of_arr, []))