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   NA P L S I I GY   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".

除斜对角线外，即：

P   A   H   NA   L   I   GY   I   R

一行中，相邻列位置相差是 2n-2。

对角线上面，即红色部分：

P   A   H   NA P L S I I GY   I   R

位置对应为j+(2n-2)-2i。 

public class DupTest {
public  static String convert(String s, int numRows) {
StringBuffer buffer=new StringBuffer();
if (s==""||s.length()==0){
return "";
}
else if((s.length()<=numRows)||s.length()==1){
return s;
}
else if(numRows==1){
return s;
}
else{
int node= 2*numRows-2;
for(int i=0;i<numRows;i++)
for(int j=i;j<s.length();j=j+node) {
buffer.append(s.charAt(j));
if (i!=0&&i!=(numRows-1)){
int m=j+node-2*i;
if(m<s.length()){
buffer.append(s.charAt(m));
}
}
}
//String buffers = buffer.toString();//将stringbuffer转化成string类型
return  buffer.toString();
} 
}


public static void main(String[] args) {
// TODO Auto-generated method stub
String s="ABcde";
int numRows=4;
System.out.println(convert(s,numRows));
}
}