Doubly-Linked Lists

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Doubly-Linked Lists

• Same basic functions operate on list
• Each node has a forward and backward link
• What advantages does a doubly-linked list offer?

88
42
109
NULL
NULL
head_ptr
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Doubly-Linked Lists

• Same basic functions operate on list
• Each node has a forward and backward link
• What advantages does a doubly-linked list offer?
• Cursor can move forwards and backwards in list.

88
42
109
NULL
NULL
head_ptr
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Stacks and Queues

• Kruse and Ryba Ch 2 and 3

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What is a stack?

• It is an ordered group of homogeneous items of
  elements.
• Elements are added to and removed from the top of
  the stack (the most recently added items are at
  the top of the stack).
• The last element to be added is the first to be
  removed (LIFO Last In, First Out).

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Stack Specification

• Definitions (provided by the user)
• MAX_ITEMS Max number of items that might be on
  the stack
• ItemType Data type of the items on the stack
• Operations
• MakeEmpty
• Boolean IsEmpty
• Boolean IsFull
• Push (ItemType newItem)
• Pop (ItemType item) (or pop and top)

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Push (ItemType newItem)

• Function Adds newItem to the top of the stack.
• Preconditions Stack has been initialized and is
  not full.
• Postconditions newItem is at the top of the
  stack.

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Pop (ItemType item)

• Function Removes topItem from stack and returns
  it in item.
• Preconditions Stack has been initialized and is
  not empty.
• Postconditions Top element has been removed from
  stack and item is a copy of the removed element.

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Stack Implementation

• include "ItemType.h"
• // Must be provided by the user of the class
• // Contains definitions for MAX_ITEMS and
  ItemType
•  
• class StackType
• public
• StackType()
• void MakeEmpty()
• bool IsEmpty() const
• bool IsFull() const
• void Push(ItemType)
• void Pop(ItemType)
• private
• int top
• ItemType itemsMAX_ITEMS

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Stack Implementation (cont.)

• StackTypeStackType()
• top -1
• void StackTypeMakeEmpty()
• top -1
• bool StackTypeIsEmpty() const
• return (top -1)

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Stack Implementation (cont.)

• bool StackTypeIsFull() const
• return (top MAX_ITEMS-1)
•  void StackTypePush(ItemType newItem)
• top
• itemstop newItem
•  void StackTypePop(ItemType item)
• item itemstop
• top--

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• Stack overflow
• The condition resulting from trying to push an
  element onto a full stack.
• if(!stack.IsFull())
• stack.Push(item)
• Stack underflow
• The condition resulting from trying to pop an
  empty stack.
• if(!stack.IsEmpty())
• stack.Pop(item)

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Implementing stacks using templates

• Templates allow the compiler to generate multiple
  versions of a class type or a function by
  allowing parameterized types.

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Implementing stacks using templates
(cont.)

• templateltclass ItemTypegt
• class StackType
• public
• StackType()
• void MakeEmpty()
• bool IsEmpty() const
• bool IsFull() const
• void Push(ItemType)
• void Pop(ItemType)
• private
• int top
• ItemType itemsMAX_ITEMS

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Example using templates

• // Client code
• StackTypeltintgt myStack
• StackTypeltfloatgt yourStack
• StackTypeltStrTypegt anotherStack
• myStack.Push(35)
• yourStack.Push(584.39)
•  
• The compiler generates distinct class types
  and gives its own internal name to each of the
  types.

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Function templates

• The definitions of the member functions must be
  rewritten as function templates.
• templateltclass ItemTypegt
• StackTypeltItemTypegtStackType()
• top -1
• templateltclass ItemTypegt
• void StackTypeltItemTypegtMakeEmpty()
• top -1

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Function templates (cont.)

•  templateltclass ItemTypegt
• bool StackTypeltItemTypegtIsEmpty() const
• return (top -1)
• templateltclass ItemTypegt
• bool StackTypeltItemTypegtIsFull() const
• return (top MAX_ITEMS-1)
•  
• templateltclass ItemTypegt
• void StackTypeltItemTypegtPush(ItemType newItem)
• top
• itemstop newItem

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Function templates (cont.)

• templateltclass ItemTypegt
• void StackTypeltItemTypegtPop(ItemType item)
• item itemstop
• top--

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Implementing stacks using dynamic array allocation

• templateltclass ItemTypegt
• class StackType
• public
• StackType(int)
• StackType()
• void MakeEmpty()
• bool IsEmpty() const
• bool IsFull() const
• void Push(ItemType)
• void Pop(ItemType)

private int top int maxStack
ItemType items
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Implementing stacks using dynamic array
allocation (cont.)

• templateltclass ItemTypegt
• StackTypeltItemTypegtStackType(int max)
• maxStack max
• top -1
• items new ItemTypemax
• templateltclass ItemTypegt
• StackTypeltItemTypegtStackType()
• delete items

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Example postfix expressions

• Postfix notation is another way of writing
  arithmetic expressions.
•  
• In postfix notation, the operator is written
  after the two operands.
•  
• infix 25 postfix 2 5
• Expressions are evaluated from left to right.
•  
• Precedence rules and parentheses are never
  needed!!

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Example postfix expressions(cont.)
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Postfix expressions Algorithm using stacks
(cont.)
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Postfix expressionsAlgorithm using stacks

• WHILE more input items exist
• Get an item
• IF item is an operand
• stack.Push(item)
• ELSE
• stack.Pop(operand2)
• stack.Pop(operand1)
• Compute result
• stack.Push(result)
• stack.Pop(result)

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• Write the body for a function that replaces each
  copy of an item in a stack with another item.
  Use the following specification. (this function
  is a client program).
• ReplaceItem(StackType stack, ItemType oldItem,
  ItemType newItem)
• Function Replaces all occurrences of oldItem
  with newItem.
• Precondition stack has been initialized.
• Postconditions Each occurrence of oldItem in
  stack has been replaced by newItem.
• (You may use any of the member functions of the
  StackType, but you may not assume any knowledge
  of how the stack is implemented).

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Stack
tempStack

• ItemType item
• StackType tempStack
• while (!Stack.IsEmpty())
• Stack.Pop(item)
• if (itemoldItem)
• tempStack.Push(newItem)
• else
• tempStack.Push(item)
• while (!tempStack.IsEmpty())
• tempStack.Pop(item)
• Stack.Push(item)

Stack
oldItem 2 newItem 5
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What is a queue?

• It is an ordered group of homogeneous items of
  elements.
• Queues have two ends
• Elements are added at one end.
• Elements are removed from the other end.
• The element added first is also removed first
  (FIFO First In, First Out).

queue
tail
head
elements enter
elements exit
2
3
4
1
no changes of order
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Queue Specification

• Definitions (provided by the user)
• MAX_ITEMS Max number of items that might be on
  the queue
• ItemType Data type of the items on the queue

• Operations
• MakeEmpty
• Boolean IsEmpty
• Boolean IsFull
• Enqueue (ItemType newItem)
• Dequeue (ItemType item) (serve and retrieve)

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Enqueue (ItemType newItem)

• Function Adds newItem to the rear of the queue.
• Preconditions Queue has been initialized and is
  not full.
• Postconditions newItem is at rear of queue.

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Dequeue (ItemType item)

• Function Removes front item from queue and
  returns it in item.
• Preconditions Queue has been initialized and is
  not empty.
• Postconditions Front element has been removed
  from queue and item is a copy of removed element.

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Implementation issues

• Implement the queue as a circular structure.
• How do we know if a queue is full or empty?
• Initialization of front and rear.
• Testing for a full or empty queue.

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Make front point to the element preceding the
front element in the queue (one memory location
will be wasted).
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Initialize front and rear
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Queue is empty now!! rear front
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Queue Implementation

• templateltclass ItemTypegt
• class QueueType
• public
• QueueType(int)
• QueueType()
• QueueType()
• void MakeEmpty()
• bool IsEmpty() const
• bool IsFull() const
• void Enqueue(ItemType)
• void Dequeue(ItemType)

private int front int rear
ItemType items int maxQue
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Queue Implementation (cont.)

• templateltclass ItemTypegt
• QueueTypeltItemTypegtQueueType(int max)
• maxQue max 1
• front maxQue - 1
• rear maxQue - 1
• items new ItemTypemaxQue

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Queue Implementation (cont.)

• templateltclass ItemTypegt
• QueueTypeltItemTypegtQueueType()
• delete items

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Queue Implementation (cont.)

• templateltclass ItemTypegt
• void QueueTypeltItemTypegt MakeEmpty()
• front maxQue - 1
• rear maxQue - 1

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Queue Implementation (cont.)

• templateltclass ItemTypegt
• bool QueueTypeltItemTypegtIsEmpty() const
• return (rear front)
• templateltclass ItemTypegt
• bool QueueTypeltItemTypegtIsFull() const
• return ( (rear 1) maxQue front)

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Queue Implementation (cont.)

• templateltclass ItemTypegt
• void QueueTypeltItemTypegtEnqueue (ItemType
  newItem)
• rear (rear 1) maxQue
• itemsrear newItem

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Queue Implementation (cont.)

• templateltclass ItemTypegt
• void QueueTypeltItemTypegtDequeue (ItemType
  item)
• front (front 1) maxQue
• item itemsfront

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Queue overflow

• The condition resulting from trying to add an
  element onto a full queue.
•  
• if(!q.IsFull())
• q.Enqueue(item)

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Queue underflow

• The condition resulting from trying to remove an
  element from an empty queue.
•  
• if(!q.IsEmpty())
• q.Dequeue(item)

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Example recognizing palindromes

• A palindrome is a string that reads the same
  forward and backward.
• Able was I ere I saw Elba 
• We will read the line of text into both a stack
  and a queue.
• Compare the contents of the stack and the queue
  character-by-character to see if they would
  produce the same string of characters.

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Example recognizing palindromes
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Example recognizing palindromes

• include ltiostream.hgt
• include ltctype.hgt
• include "stack.h"
• include "queue.h
• int main()
• StackTypeltchargt s
• QueTypeltchargt q
• char ch
• char sItem, qItem
• int mismatches 0

cout ltlt "Enter string " ltlt endl  
while(cin.peek() ! '\\n')   cin gtgt ch
if(isalpha(ch))   if(!s.IsFull())
s.Push(toupper(ch))   if(!q.IsFull())
q.Enqueue(toupper(ch))
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Example recognizing palindromes

• while( (!q.IsEmpty()) (!s.IsEmpty()) )
• s.Pop(sItem)
• q.Dequeue(qItem)
•  
• if(sItem ! qItem)
• mismatches
• if (mismatches 0)
• cout ltlt "That is a palindrome" ltlt endl
• else
• cout ltlt That is not a palindrome" ltlt endl
•  
• return 0

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Case Study Simulation

• Queuing System consists of servers and queues of
  objects to be served.
• Simulation a program that determines how long
  items must wait in line before being served.

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Case Study Simulation (cont.)

• Inputs to the simulation
• (1) the length of the simulation
• (2) the average transaction time
• (3) the number of servers
• (4) the average time between job arrivals

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Case Study Simulation (cont.)

• Parameters the simulation must vary
• (1) number of servers
• (2) time between arrivals of items
•  
• Output of simulation average wait time.

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