head of a Q is the next item to be removed
tail of a Q is the next slot to get a new item

   0      1     2     3
                          head = 0, size = 0, (tail = 0)
// insert A
   A                      head = 0, size = 1, (tail = 1)
// insert B
   A      B               head = 0, size = 2, (tail = 2)
// remove an item
   A      B               head = 1, size = 1, (tail = 2)
// insert C
   A      B     C         head = 1, size = 2, (tail = 3)
// insert D
   A      B     C     D   head = 1, size = 3, (tail = 0)
// insert E
   E      B     C     D   head = 1, size = 4, (tail = 1)
// remove an item
   E      B     C     D   head = 2, size = 3, (tail = 1)
// insert F
   E      F     C     D   head = 2, size = 4, (tail = 2)
// insert G (and trigger ArrayADT resize)
   0      1     2     3     4     5     6     7
   E      F     C     D                             head = 2, size = 4, (tail = 2)
// solution 1: move the portion that has not wrapped around
   E      F     C     D                 C     D     head = 6, size = 4, (tail = 2)
   E      F     G     D                 C     D     head = 6, size = 5, (tail = 3)
// solution 2: move the portion that has wrapped around
   E      F     C     D     E     F                 head = 2, size = 4, (tail = 6)
   E      F     C     D     E     F     G           head = 2, size = 5, (tail = 7)


How do we resize?

Solution 2 is better because it does not need to know the new capacity. As we change array elements, the new capacity is automatically adjusted.
   
   
tail = (head + size) % capacity