CIS 403503 Accelerated DataFile Structures

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CIS 403/503Accelerated Data-File Structures

• Lecture 15
• Queue

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Objectives

• In this lecture, we will learn
• Stack application Prefix, infix, postfix
• Queue

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Stack Application
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Mathematical Expression

• Infix a b c
• Postfix abc
• Examples
• (ab)c //abc
• (abc)/de
• ab-c/d
• abcdef
• a(bcd)/e
• (bb-4ac)/(2a)

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Infix-to-Postfix

• Push operators onto a stack
• Output operands to the postfix string
• Example a b c
• What about ab/cd

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Infix-to-Postfix

• Remove all operators on the stack that have the
  same or higher precedence
• Example ab/cd
• What about abc

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Infix-to-Postfix

• Right-assocative
• Input precedence
• Stack precedence
• If the input precedence is lt stack precedence,
  pop the operator and write it to the postfix
• If the input precedence is gt stack precedence,
  push the operator on the stack,

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Infix-to-Postfix

• and -
• Input 1
• Stack 1
• Rank -1
• , / and
• Input 2
• Stack 2
• Rank -1

• Input 4
• Stack 3
• Rank -1
• (
• Input 5
• Stack -1
• Rank 0

• )
• Input 0
• Stack 0
• Rank 0

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Infix-to-Postfix

• 3 (4 - 25)6
• 5 (23)6

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Queue
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Overview

• Queue
• A data structure in which data are added to the
  back and removed from the front
• FIFO/FCFS

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STL Queue Operations

• void push(const T item)
• Insert item at the top
• Postcondition new item at the back
• void pop()
• Remove the item from the front
• Precondition queue is not empty
• Postcondition queue has one less item
• bool empty() const
• Check if queue is empty
• int size() const
• Number of items in the queue
• T front()
• A reference to the front of the queue
• Precondition queue is not empty
• const T front() const
• Constant reference

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Example

• includeltqueuegt
• includeltiostreamgt
• using namespace std
• int main()
• queueltintgt q
• int i
• for (i1 ilt5 i)
• q.push(i)
• cout ltlt Queue size " ltlt q.size() ltlt
  endl
• cout ltlt Pop the queue" ltlt endl
• while(!q.empty())
• cout ltlt q.front() ltlt " "
• q.pop()
• cout ltlt endl

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Example

• includeltqueuegt
• includeltiostreamgt
• using namespace std
• int main()
• queueltintgt q
• q.push(2)
• q.push(3)
• q.push(-1)
• cout ltltq.top() ltlt endl
• //change top to 4
• q.front() 5
• while(!q.empty())
• cout ltlt q.front() ltlt " "
• q.pop()

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Summary

• Stack application infix-to-postfix
• Queue ADT

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Possible Quiz Questions

• Convert from infix to postfix
• Stack operation in the design of infix-to-postfix
  conversion
• Queue operations in STL