1. Basic Data Types Queues
Richard Newman
Based on Sedgewick and Wayne 1

2. Stacks and Queues Stacks Dynamic Resizing Queues Generics Iterators
Applications 2

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? 3

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. 4

5. Queue API Public class Queue: Can be any type (stay tuned) ENQUEUE
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 5

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 q[++tail]
dequeue() remove item from q[head++]
Update (increment) head and tail modulo capacity
q[] it
was
the
best of
head 1 2 3 4 5
tail

10. Queues: array implementation
enqueue() add new item at q[++tail]
q[] it
was
the
best of
times 1 2 3 4 5 6
head
tail

11. Queues: array implementation
dequeue() remove item from q[head++]
q[] it
was
the
best of
times 1 2 3 4 5 6
head
tail

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

13. Dynamic Resizing Queues: 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