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The template The template parameter is the parameter is the type of the items type of the items that can be put in that can be put in the queue.. Array Implementation[r]
(1)Chapter 8 introduces the Chapter 8 introduces the
queue
queue data type.data type Several example Several example
applications of queues are applications of queues are
given in that chapter. given in that chapter.
This presentation describes This presentation describes
the queue operations and the queue operations and two ways to implement a two ways to implement a
queue queue Data Structures
(2)The Queue Operations
A queue is like a line A queue is like a line
of people waiting for a of people waiting for a bank teller. The queue bank teller. The queue
has a
has a frontfront and a and a rearrear..
$ $
(3)New people must enter the queue at the New people must enter the queue at the
rear. The C++ queue class calls this a rear. The C++ queue class calls this a
push
push, although it is usually called an , although it is usually called an enqueue
enqueue operation. operation
$ $
(4)The Queue Operations
When an item is taken from the queue, When an item is taken from the queue,
it always comes from the front. The it always comes from the front. The
C++ queue calls this a
C++ queue calls this a poppop, although it , although it is usually called a
is usually called a dequeuedequeue operation. operation.
$ $
(5)The C++ standard The C++ standard template library has template library has a queue template a queue template class class The template The template parameter is the parameter is the type of the items type of the items that can be put in that can be put in the queue the queue template <class Item> class queue<Item>
(6)Array Implementation
A queue can be implemented with an array, as A queue can be implemented with an array, as
shown here. For example, this queue contains the shown here. For example, this queue contains the
integers 4 (at the front), 8 and 6 (at the rear) integers 4 (at the front), 8 and 6 (at the rear)
[ 0 ]
[ 0 ] [1][1] [ 2 ][ 2 ] [ 3 ][ 3 ] [ 4 ][ 4 ] [ 5 ][ 5 ] . . .. . .
An array of integers
An array of integers
to implement a
to implement a
queue of integers
queue of integers
4
We don't care what's in
We don't care what's in
this part of the array
(7)The easiest implementation also keeps The easiest implementation also keeps
track of the number of items in the track of the number of items in the
queue and the index of the first queue and the index of the first
element (at the front of the queue), the element (at the front of the queue), the
last element (at the rear) last element (at the rear)
[ 0 ]
[ 0 ] [1][1] [ 2 ][ 2 ] [ 3 ][ 3 ] [ 4 ][ 4 ] [ 5 ][ 5 ] . . .. . .
4
3
first
first
0
last
last