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 s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:

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

class Solution:
    def convert(self, s, numRows):
        """
        :type s: str
        :type numRows: int
        :rtype: str
        """
        l = ['' for _ in range(numRows)]
        if numRows == 1:
            return s
        total = 2*(numRows-1)
        for i in range(len(s)):
            pos = i % total
            if pos > numRows-1:
                pos = total - pos
            l[pos] += s[i]
        res = ''
        for i in range(numRows):
            res += l[i]
        return res

不需要初始化整个矩阵，只需要初始化一个一维list，l[i]保存的是第i行的情况。