【LeetCode 6. 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);

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

翻译:

字符串“ PAYPALISHIRING”以Z字形模式写在给定的行数上，如下所示：（您可能希望以固定字体显示此模式以提高可读性）

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

然后一行一行地读取：“ PAHNAPLSIIGYIR”

编写代码，该代码将包含一个字符串，并根据行数进行此转换：

Kotlin代码实现：

 fun convert(s:String,numRows: Int):String{
   if(numRows<2) return s
    val rows = arrayListOf<StringBuilder>()
    for (i in 0 until numRows) {
        rows.add(StringBuilder())
    }
    
    var i=0
    var flag=-1
    for (c :Char in s.toCharArray()){
        rows[i].append(c)
        if(i==0||i==numRows-1) flag=-flag
        i+=flag
    }

    val res=StringBuilder()
    for (row :StringBuilder in rows){
        res.append(row)
    }
}

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