1 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)

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".
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 String
 
2 思路：
2.1 什么是zigzag？
2.2 解决方法：需要使用nRows个StringBuffer来存储每列的字符，最后再循环一遍即可，参考：https://leetcode.com/discuss/10493/easy-to-understand-java-solution
 
3 代码：
public String convert(String s, int nRows) {
        char[] chars = s.toCharArray();
        StringBuffer[] sbs = new StringBuffer[nRows+1];
        for(int i = 0; i <= nRows ; i++){
            sbs[i] = new StringBuffer("");
        }
        
        int index = 0;
        int len = s.length();
        while(index < len){
            for(int i = 1; i <= nRows && index < len ; i++){
                sbs[i].append(chars[index++]);           // vertical down
            }
            
            for(int i = nRows - 2; i > 0 && index < len ; i--){
                sbs[i+1].append(chars[index++]);          //angle up
            }
        }
        
        for(int i = 1; i <= nRows; i++){
            sbs[0].append(sbs[i]);
        }
        
        return sbs[0].toString();
    }