看了别人的，然后自己重新写了一遍理解了，但是目前没有再想到更好的解决办法。

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

Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);

class Solution {
    public String convert(String s, int numRows) {
        if(s==null||s.length()==0||numRows<=0){
        	return "";
        }
        if(numRows==1)
        	return s;
        StringBuilder res=new StringBuilder();
        int size=2*numRows-2;
        for(int i=0;i<numRows;i++){
        	for(int j=i;j<s.length();j+=size){
        		res.append(s.charAt(j));
        		if(i!=0&&i!=numRows-1){
        			int tmp=j+size-2*i;
        			if(tmp<s.length())
        				res.append(s.charAt(tmp));
        		}
        	}
        }
        return res.toString();
    }
}