Queue Using Circular Linked Lists

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QueueUsing Circular Linked Lists
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UWP - Qi Yang
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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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Queue Using a Linked Listwith Two Pointers
. . .
front
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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 )

Can we remove the if statement? Assuming rear
is invalid (null) if front is null
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• Assuming rear is invalid (null) if front is null
• public class QueueltEgt
•   . . .
• public void add ( E x )
• if ( front null )
• rear front new Node ( x, null )
• else
• rear rear.next new Node ( x, null )
•  
• public E remove()
• if ( front null )
• return null
• E x front.info
• front front.next
• return x

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Queue Using a Linked Listwith One Pointer
. . .
front
Method remove O(1)
Method add O(N)
. . .
Method remove How to find front? Circular
Linked List O(1)
Method add O(1)
rear.next is front!
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Queue Using a Linked Listwith One Pointer
Queue with one item if (rear rear.next)
Empty queue if (rear null)
Queue with two or more items if (rear !
rear.next)
. . .
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Empty Queue
Empty queue if (rear null)
Remove Do nothing Add rear new
Node( obj, null ) rear.next rear
Can it be one line? rear.next rear new
Node(obj, null) NO! Java examines rear.next
first rear.next is not a variable
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Queue with One Item
Queue with one item if (rear rear.next)
Remove rear null Add new Node( obj,
rear ) rear.next new Node( obj, rear )
rear rear.next new Node( obj, rear
.next) rear.next new Node( obj, rear
.next) rear rear.next rear rear.next
new Node( obj, rear .next)
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Queue with Two or More Items
Remove rear.next rear.next.next Add
new Node( obj, rear.next ) rear.next new
Node( obj, rear.next ) rear rear.next
rear rear.next new Node( obj, rear.next )
. . .
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• public class QueueltEgt
• . . .
• public void add ( E x )
• if ( rear null )
• rear new Node ( x, null )
• rear.next rear
• else
• rear rear.next new Node ( x,
  rear.next )
•  
• . . .

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• public class QueueltEgt
• . . .
• public E remove()
• if ( rear null )
• return null
• E x rear.next.info
• if ( rear rear.next )
• rear null
• else
• rear.next rear.next.next
• return x

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Quiz 6

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