6. ZigZag Conversion

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本文介绍了一种将字符串以Z字形排列并按行读取的算法实现。通过使用多个字符串来记录每一行的内容，并根据当前方向进行切换，最终合并所有行得到目标字符串。

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

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);

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

The idea is just clear: use numRows character strings to record characters in each row. Traverse the original string s, we need to know which direction are we going, up or down, use True or False to represent this status. Finally, merge all rows.

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
        rows = ['' for _ in range(numRows)]
        curr = [0, True]
        for char in s:
            rows[curr[0]] += char
            if curr[1]:
                curr[0] += 1
            else:
                curr[0] -= 1
            if curr[0] == 0:
                curr[1] = True
            if curr[0] == numRows - 1:
                curr[1] = False
        return ''.join(rows)