Stack and Queue Using Linked Lists

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Stack and QueueUsing Linked Lists
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UWP - Qi Yang
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Stack Upside-Down
8 7 6 5 4 3 2 1 0
top
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Implementing Stack Using Array

• public class Stack
• private Object items
• private int top 0
• public Stack( int size )
• items new Objectsize
• public void push ( Object obj )
• itemstop obj
• public Object pop()
• return items--top
• . . .

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Implementing Stack Using Linked List

• The signatures of the methods should stay the
  same
• The implementation shouldn't matter to the user
  as long as it is correct and efficient
• Should "top" be the front or back?
• Whats the Big O for pop and push?
• if top is front
• O(1)
• if top is back
• O(n)
• So top should be front!

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• Top is front
• push insert at front
• top new Node(obj, top)
• pop remove from front
• top top.next

. . .
. . .
top
. . .
top
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Implementing Stack Using Linked List

• public class Stack
• Node top
• public Stack()
• top null
• public void push ( Object obj )
• top new Node(obj, top)
• public Object pop()
• Object tmp top.info
• top top.next
• return tmp
• . . .

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Queue Class

• Make the array circular

front points to where the first element is
rear points to where next element goes
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public class Queue private Object items
private int front, rear, count ...
public void add ( Object x )
itemsrear x rear (rear 1)
items.length count public
Object remove() Object x
itemsfront front (front 1)
items.length count -- return x
// class Queue
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Queue Using a Linked List

• Two pointers front and rear
• Both add and remove are O(1).
• Note we make class Node private, so no access
  outside the class.
• Make the Queue generic it doesnt get the
  warnings that the generic array implementation
  gave

. . .
front
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• public class QueueltEgt
• // treat as a dumb struct, but private to
  Queue
• private class Node
• public E info
• public Node next
• public Node ( E x, Node p )
• info x
• next p
•   private Node front rear null
• public boolean isEmpty()
• return front null
•   . . .

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• add (at rear)
• rear.next new Node ( x, null )
• rear rear.next
• remove (at front)
• tmp front.info
• front front.next

. . .
front
tmp
. . .
front
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• public class QueueltEgt
•   . . .
• public void add ( E x ) // add at the end
• if ( front null )
• front new Node ( x, null )
• rear front
• else
• rear.next new Node ( x, null )
• rear rear.next
•  
• public E remove() // remove from the front
• if ( front null )

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Quiz 5
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Quiz 6

• Hashing
• Division (remainder)
• Collision
• Linear Probe
• Double hash
• Buckets
• Binary Search
• Linked List
• Add and remove

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Prog6

• Inheritance
• Polymorphysm
• Class PFigure
• Move
• Other methods

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Lab 8