6. ZigZag Conversion(JAVA)

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"

.

代码：

public class Solution {
    public String convert(String s, int numRows) {
        String row_start[]=new String[numRows];
        String str="";
        
        if(numRows==1)return s;
        
        int i=0,j=0;
        int step=numRows-2;
        
        for(i=0;i<numRows;i++)
        {
            row_start[i]="";
        }
        
        i=0;
        while(i < s.length())
        {
            for(j=0;i<s.length() && j<numRows;j++)
            {
                row_start[j]+=s.charAt(i++);
            }
            
            for(j=step;i<s.length() && j>0;--j)
            {
                row_start[j]+=s.charAt(i++);
            }
        }
        
        for(i=0;i<numRows;i++)
        {
            if(row_start[i]!=null)
                str+=row_start[i];
        }
        
        return str;
    }
}