6. ZigZag Conversion

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

Solution:

import itertools


class Solution(object):
    def convert(self, s, numRows):
        """
        :type s: str
        :type numRows: int
        :rtype: str
        """
        indices = itertools.cycle(range(numRows) + range(numRows - 2, 0, -1))
        rows = [[] for _ in xrange(numRows)]
        for idx, char in itertools.izip(indices, s):
            rows[idx].append(char)
        return ''.join(itertools.chain(*rows))