Training

1
Basic Data TypesQueues
Richard Newman Based on Sedgewick and Wayne
2
Stacks and Queues

• Stacks
• Dynamic Resizing
• Queues
• Generics
• Iterators
• Applications

3
Fundamental data types
Values sets of objects
Operations insert, remove, test if
empty. Intent is clear when we insert. Which
item do we remove?
4
Fundamental data types
Stack Remove the item most recently
added. (LIFO last in first out) Analogy
Cafeteria trays. Web surfing. Queue Remove the
item least recently added. (FIFO first in
first out) Analogy Grocery store checkout line.
5
Queue API
Public class Queue Can be any type (stay
tuned) Queue ( ) Create an empty queue Void
enqueue (String S) Insert a new item onto
stack String dequeue ( ) Remove and return
the item least recently added Boolean isEmpty
( ) Is the queue empty?
ENQUEUE
DEQUEUE
NEWEST
OLDEST
6
Queue linked-list implementation
Can it be done with a singly linked list? a) No
not efficiently b) c) d) IDK
Most recent
Least recent
of
best
the
was
it
Most recent
Least recent
of
best
the
was
it
7
Dequeue linked-list implementation
tail
head
of
best
the
was
it
String item head.item
it
tail
head
of
best
the
was
it
head head.next
tail
head
of
best
the
was
return item
it
8
Enqueue linked-list implementation
tail
oldTail
head
best
the
was
it
Node oldTail tail
tail
oldTail
head
of
best
the
was
it
tail new Node() tail.item of
tail
oldTail
head
of
best
the
was
it
oldTail.next tail
9
Queues array implementation
Use array q to store items in
queue enqueue() add new item at
qtail dequeue() remove item from
qhead Update (increment) head and tail
modulo capacity
of
best
the
was
it
q
0 head
1
2
3
4
5 tail
10
Queues array implementation
enqueue() add new item at qtail
q
of
best
the
was
it


times
1
2
3
4
5
6
0
head
tail
11
Queues array implementation
dequeue() remove item from qhead
of
best
the
was
it
q


times
1
2
3
4
5
6
0
head
tail
12
Queues array implementation
Update (increment) head and tail modulo capacity
(7)
of
best
the
was
q


times
it
was
1
2
3
4
5
6
0
head
tail
13
Dynamic ResizingQueues array implementation
Arrays are instantiated with a specific size Q
How to grow queue when capacity reached? Q When
to shrink array when queue shrinks? A What do
you think? )
14
Next Generics