案例来自:http://www.cnblogs.com/vajoy/p/5095511.html;

效果展示:

代码展示:

1  2  3  4      5     42     47 48 49   
      
       50     
       
        51         
        
         52             
         
          53                 
          
           54                     
           55                 
          56             
         57             
         
          58 59                 
          60                 
          61 62             
         63         
        64 65     
       
66 
      67 68