public static char[][] build_zigzag_block(String plain,int row)
	{
		char[][] result=new char[row][plain.length()];
		int position=0;
		boolean down=true;
		for(int i=0;i<plain.length();i++)
		{
			result[position][i]=plain.charAt(i);
			if(down)
			{
				if(position==row-1)
				{
					down=false;
					position--;
				}
				else
				{
					position++;
				}
			}
			else
			{
				if(position==0)
				{
					down=true;
					position++;
				}
				else
				{
				  position--;
				}
			}
		}
		return result;
	}