Problem of the Day

Bezout acquired 19 camels through his trading skill,“Of the collected camels,” it said in the late merchant’s will,“Exactly half go to my first son, Abdul,One-fourth to Wasim, one-fifth to Rasul,Call a wise man to distribute — don’t sell or kill.”

How does the Wise Man do it?

Problem of the Day

Bezout acquired 19 camels through his trading skill,“Of the collected camels,” it said in the late merchant’s will,“Exactly half go to my first son, Abdul,One-fourth to Wasim, one-fifth to Rasul,Call a wise man to distribute — don’t sell or kill.”

How does the Wise Man do it?The Wise Man adds his own camel (making 20 to distribute)

Abdul gets 10 (20 * 0.5)Wasim gets 5 (20 * 0.25)Rasul gets 4 (20 * 0.2)

& Wise Man gets his camel back (20 – 10 – 5 – 4 = 1)

LECTURE 25: DEQUES

CSC 212 – Data Structures

Stack Memory Aid

Roses are red and violets are blue

Implement push, peek, & pop

And you’re a Stack too!

Stack Interface

public interface Stack<E> extends Collection {public E peek() throws EmptyCollectionException;public E pop() throws EmptyCollectionException;public void push(E element);

}

Queue Memory Aid

Queue Memory AidIt’s hard writing

rhymes with enqueue,

dequeue, and first

Queue Memory Aid

Queue ADT

public interface Queue<E> extends Collection {public E first() throws EmptyCollectionException;public E dequeue() throws EmptyCollectionException;public void enqueue(E element);

}

Stacks vs. Queues

Access data with Stack in LIFO order Last In-First Out ordering is unfair

(unless late) Data accessed in Queue using FIFO

orderFirst In-First Out is first-come, first-

served

Stacks vs. Queues

Access data with Stack in LIFO order Last In-First Out ordering is unfair

(unless late) Data accessed in Queue using FIFO

orderFirst In-First Out is first-come, first-

served

Ord

er re

ad if

Que

ue

Stacks vs. Queues

Access data with Stack in LIFO order Last In-First Out ordering is unfair

(unless late) Data accessed in Queue using FIFO

orderFirst In-First Out is first-come, first-

served

Ord

er re

ad if

Que

ueO

rder read if Stack

Cannot access both sides of either Collection Transplant waiting lists Help center phone banks My Grandpa dealing cards for money

Stack only works with one end Add & remove from top of the Stack

Queue limits how each side used Front provides access & removal of elements Must use the Queue’s end to add elements

Still Have Limits

Pronounced “deck” (like on a house) Mnemonic for Double Ended QUEue dequeue ≠ deque and do not sound alike

Structure that provides access to both ends Combines Stack & Queue concepts Is also able to add elements to start

Deque ADT

public interface Deque<E> extends Collection { /* first() */ public E peekFirst() throws EmptyCollectionException;

/* peek() */ public E peekLast() throws EmptyCollectionException;

/* dequeue() */ public E removeFirst() throws EmptyCollectionException;

/* pop() */ public E removeLast() throws EmptyCollectionException;

/* push() or enqueue() */ public addLast(E elem);

/* brand new method! */ public addFirst(E elem);

}

Deque Interface

VIPs versus Losers

Linked-list based Deque

head rear

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

retVal

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

retVal

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

retVal

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

retVal

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

newElem

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

newElem

newNode

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

newElem

newNode

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

newElem

newNode

Class defines fields aliased to first & last nodes Doubly-linked list enables O(1) time for all

methods Add elements by adding new Node at end Move end node & set next/previous to

remove element

Linked-list based Deque

head rear

Did you see why doubly-linked list is important?

Why Doubly-Linked?

head rear

Did you see why doubly-linked list is important? New or next node aliased by Queue’s fields Stack set up so we only ever move to next

node

Why Doubly-Linked?

head rear

Did you see why doubly-linked list is important? New or next node aliased by Queue’s fields Stack set up so we only ever move to next

node Deque moves forward & backward; needs

dual links

Why Doubly-Linked?

head rear

Your Turn

Get into your groups and complete activity

For Next Lecture

Project #1 is due by 11:59PM tomorrow Can use 1 or both virtual extensions on this

project Check with me if uncertain how many

you’ve used

Midterm #2 will be in class on Monday