[Leetcode][python]ZigZag Conversion/Z字形变换

class Solution(object):
    def convert(self, s, numRows):
        """
        :type s: str
        :type numRows: int
        :rtype: str
        """
        if numRows == 1 or numRows >= len(s):
            return s
        zigzag = [[] for x in range(numRows)]
        row, step = 0, 1
        for c in s:
            zigzag[row] += c,
            if row == 0:
                step = 1
            elif row == numRows - 1:
                step = -1
            row += step
        # return ''.join(reduce(operator.add, zigzag))
        # [[u'P', u'A', u'H', u'N'], [u'A', u'P', u'L', u'S', u'I', u'I', u'G'], [u'Y', u'I', u'R']]
        result = ''
        for i in range(len(zigzag)): 
            result += ''.join(zigzag[i])  # list拼接为字符串 
        return result