-5 -3 -1 1 3 5 7 9 

-3 -1 1 3 5 7 9 8 

-3 -1 1 5 9 

-1 5 9 

front = -1

back = 9

find 5: 5
size = 3



Good that front() is NULL
Good that back() is NULL
<no data> <no data> <no data> 
size = 3
101 <no data> <no data> <no data> 999 
size = 5

front = 101

back = 999