size = 12
front = 42
back = 86
0 1 2 3 4 5 6 7 8 9 -999 -999 -999 -999 -999 -72 2 9 
after erase 2
0 2 3 4 5 6 7 8 9 -72 2 9 
-72 0 2 2 3 4 5 6 7 8 9 9 
19 -7 -72 0 2 2 3 4 5 6 7 8 9 9 113 
19 -7 -72 0 2 3 4 5 6 7 8 9 113 
113 19 9 8 7 6 5 4 3 2 0 -7 -72