                  50  60  70  80
                  ĿĿĿĿ
                          
                          
                          
                          
                  
                  58  68  78  88
                  ĿĿĿĿ
                          
                          
                          
                          
                  

50>buffer
60>50
70>60
80>70
58>80
68>58
78>68
88>78
buffer>88
