题目

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)

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：

  Input: s= "ABCDEFGHIJKLMNOP", numRows = 4,

  Output:AGMBFHLNCEIKODJP

  Explanation：

    A G M

    B F H L N

    C E I K O

    D J P

思路：

先将字符串\(s\)进行Z字排列，再按行读取字符。将Z字分为上中下三个部分，则例子的Z上：ABCD，中：EF，下:GHIJ。分析其规律可以发现，对于指定的行数\(n\)，中部的个数为\(n-2\)，将每一个上+中作为一个循环，则循环周期为\(t=n+n-2\)。于是有

第1行：\(s[0], s[0+t],s[0+2 \cdot t], \cdots ;\)

第2行：\(s[1], s[0+t-1],s[1+t],\cdots;\)

\(\cdots\)

第\(n\)行：\(s[n-1],s[n-1+t],s[n-1+2 \cdot t]\cdots .\)

C++

class solution{public:  string convert(string s, int numRows){    if(s.size()==1) return s;    string resString;    int stringLen=s.size();    int cycleLen=2*numRows-2;    for(int i=0;i

python

class Solution(object):    def convert(self, s, numRows):        """        :type s: str        :type numRows: int        :rtype: str        """                if numRows == 1:            return s                rows = [""]*numRows                cycle = 2*numRows - 2        result = ""                level = 0 #层数        aux = -1        for i in s:            rows[level] += i            if(level == 0 or level == numRows -1):                aux *= -1            level += aux                for i in rows:            result += i                            return result