CMSC 341

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CMSC 341

• Deques, Stacks and Queues

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The Double-Ended Queue ADT

• The double ended queue is referred to as a Deque
  (rhymes with check)
• Restricted List
• add to the end
• remove from the end
• add to the front
• remove from the front
• Stacks and Queues are often implemented using a
  Deque

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insertAtFront
removeFromBack
removeFromFront
insertAtBack
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Front
Back
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insertAtFront(10)
10
Front
Back
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insertAtFront(5)
Front
Back
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insertAtBack(20)
Front
Back
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insertAtBack(removeFromFront())
Front
Back
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Adapting Lists to Implement Deques

• List interface (Weiss)
• Does not directly support Deque operations
• Could support them with a little extra code
• Any good list interface will support Deque
  operations
• Adapter Design Pattern
• Allow a client to use a class whose interface is
  different from the one expected by the client
• Do not modify client or class, write adapter
  class that sits between them

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Client
theDeque.insertAtFront(10)
Deque (adapter)
theList.insert(10, theList.zeroth())
List (adaptee)
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Deque.H

• include LinkedList.H
• template ltclass Objectgt
• class Deque
• public
• Deque()
• Deque(const Deque deq)
• Deque()
• bool isEmpty() const
• void makeEmpty()
• void insertAtFront(const Object x)
• void insertAtBack(const Object x)
• Object removeFromFront()
• Object rremoveFromBack()
• const Deque operator(const Deque deq)

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Deque.H (cont)

• private
• ListltObjectgt _theList

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New List Methods Assumed to Exist

• ListItrltObjectgt last()
• Returns iterator point to last object in list
• remove(ListItrltObjectgt itr)
• Removes the object pointed to by itr
• What is the state of itr after remove?
• What are the complexity of last() and remove()?
• Singly linked
• Doubly linked

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Deque.C

• template ltclass Objectgt
• DequeltObjectgtDeque()
• template ltclass Objectgt
• DequeltObjectgtDeque(const Deque deq)
• _theList deq._theList
• template ltclass Objectgt
• DequeltObjectgtDeque()

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Deque.C (cont)

• template ltclass Objectgt
• bool DequeltObjectgtisEmpty() const
• return _theList.isEmpty()
• template ltclass Objectgt
• void DequeltObjectgtmakeEmpty ()
• _theList.makeEmpty()

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Deque.C (cont)

• template ltclass Objectgt
• Object DequeltObjectgtremoveFromFront()
• if (isEmpty())
• throw DequeException(remove on empty deque)
• Object tmp _theList.zeroth().retrieve()
• _theList.remove(_theList.zeroth())
• return tmp
• template ltclass Objectgt
• void DequeltObjectgtinsertAtFront(const Object
  x)
• _theList.insert(x, _theList.zeroth())

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Deque.C (cont)

• template ltclass Objectgt
• Object DequeltObjectgtremoveFromBack()
• if (isEmpty())
• throw DequeException(remove on empty deque)
• Object tmp _theList.last().retrieve()
• _theList.remove(_theList.last())
• return tmp
• template ltclass Objectgt
• void DequeltObjectgtinsertAtBack(const Object x)
  
• _theList.insert(x, _theList.last())

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Deque.C (cont)

• template ltclass Objectgt
• const DequeltObjectgt DequeltObjectgt
• operator(const Deque deq)
• if (this ! deq)
• _theList deq._theList
• return this

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DequeException.H

• class DequeException
• public
• DequeException() // Message is the empty
  string
• DequeException(const string errorMsg)
• DequeException(const DequeException ce)
• DequeException()
• const DequeException
• operator(const DequeException ce)
• const string errorMsg() const // Accessor for
  msg
• private
• string _msg

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DequeException.C

• DequeExceptionDequeException()
• DequeExceptionDequeException(const string
  errorMsg)
• _msg errorMsg
• DequeExceptionDequeException(const
  DequeException ce)
• _msg ce.errorMsg()
• DequeExceptionDequeException()

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DequeException.C (cont)

• const DequeException
• DequeExceptionoperator(const DequeException
  ce)
• if (this ce)
• return this // don't assign to itself
• _msg ce.errorMsg()
• return this
• const string DequeExceptionerrorMsg() const
• return _msg

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TestDeque.C

• int main ()
• Dequeltintgt deq
• deq.insertAtBack(1)
• deq.insertAtBack(2)
• printDeque(deq)
• Dequeltintgt otherdeq
• otherdeq deq
• printDeque(otherdeq)
• cout ltlt deq.removeFromFront() ltlt endl
• cout ltlt deq.removeFromFront() ltlt endl

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TestDeque.C (cont)

• printDeque(deq)
• printDeque(otherdeq)
• try
• deq.removeFromFront()
• catch (DequeException e)
• cout ltlt e.errorMsg() ltlt endl

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Queue ADT

• Restricted List
• only add to end
• only remove from front
• Examples
• line waiting for service
• jobs waiting to print
• Implement using a Deque

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Queue.H

• template ltclass Objectgt
• class Queue
• public
• Queue()
• Queue()
• bool isEmpty() const
• void makeEmpty()Object dequeue()void enqueue
  (const Object x)
• private
• DequeltObjectgt _theDeque

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Queue.C

• template ltclass Objectgt
• QueueltObjectgtQueue()
• Template ltclass Objectgt
• QueueltObjectgtQueue()
• template ltclass Objectgt
• void QueueltObjectgtmakeEmpty( )
• _theDeque.makeEmpty()

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Queue.C (contd)

• template ltclass Objectgt
• void QueueltObjectgtenqueue(const Object x)
• _theDeque.insertAtBack(x)
• template ltclass Objectgt
• Object QueueltObjectgtdequeue()
• return _theDeque.removeFromFront(x)

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An Alternative Queue.H

• template ltclass Objectgt
• class Queue
• public
• Queue(int capacity10)
• Queue()
• bool isEmpty() const
• void makeEmpty()Object dequeue()void enqueue
  (const Object x)
• private
• vectorltObjectgt theArray
• int currentSize
• int front
• int back
• void increment (int x)

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Queue.C

• template ltclass Objectgt
• QueueltObjectgtQueue( int capacity ) theArray(
  capacity )
• makeEmpty( )
• template ltclass Objectgt
• void QueueltObjectgtmakeEmpty( )
• currentSize 0
• front 0
• back -1

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Queue.C (contd)

• template ltclass Objectgt
• void QueueltObjectgtenqueue(const Object x)
• if (isFull())
• throw Overflow()
• increment (back)
• theArrayback x
• currentSize
• template ltclass Objectgt
• void QueueltObjectgtincrement(int x)
• if (x theArray.size())
• x 0

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Queue.C (cont)

• template ltclass Objectgt
• Object QueueltObjectgtdequeue()
• if (isEmpty())
• throw Underflow()
• currentSize--
• Object frontItem theArrayfront
• increment(front)
• return frontItem

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theArray
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Stack ADT

• Restricted List
• only add to top
• only remove from top
• Examples
• pile of trays
• partial results
• local state
• Implement using a Deque

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Stack.H

• template ltclass Objectgt
• class Stack
• public
• Stack()
• Stack()
• bool isEmpty() const
• void makeEmpty()
• Object pop()
• void push(const Object x)
• private
• DequeueltObjectgt _theDeque

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Stack.C

• template ltclass Objectgt
• StackltObjectgtStack()
• Template ltclass Objectgt
• StackltObjectgtStack()
• template ltclass Objectgt
• void StackltObjectgtmakeEmpty( )
• _theDeque.makeEmpty()

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Stack.C (contd)

• template ltclass Objectgt
• void QueueltObjectgtpush(const Object x)
• _theDeque.insertAtFont(x)
• template ltclass Objectgt
• Object QueueltObjectgtpop()
• return _theDeque.removeFromFront(x)