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 text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

分析：https://segmentfault.com/a/1190000005751185

打印题，二话不说，画图，标数字，找规律。
这题其实是EPI这本书里7.11题(Write a string sinusoidally)，书里的题规定k=3,在leetcode里k作为参数，所以更难了。
leetcode的这个例子的图非常反人类，其实可以把它画得优美一些，像正弦函数的波浪形：

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

举个别的例子自己画一下：

 public class Solution {
     public String convert(String s, int nRows) {

         StringBuffer[] sb = new StringBuffer[nRows];
         for (int i = ; i < sb.length; i++) {
             sb[i] = new StringBuffer();
         }

         int i = ;
         while (i < s.length()) {
             for (int idx = ; idx < nRows && i < s.length(); idx++) // vertically down
                 sb[idx].append(s.charAt(i++));
             for (int idx = nRows-; idx >=  && i < s.length(); idx--) // obliquely up
                 sb[idx].append(s.charAt(i++));
         }
         for (int idx = ; idx < sb.length; idx++)
             sb[].append(sb[idx]);
         return sb[].toString();
     }
 }