Stacks, Queues, and Linked Lists

1
Stacks, Queues, and Linked Lists

• Stacks (Last in/First out List)
• Operations Push, Pop, Test Empty, Test Full,
  Peek, Size
• Queue(First in/First out List)
• Operations Insert, Remove, Test Empty, Test
  Full, Peek, Size
• Linked List(A list of elements connected by
  pointers)
• Insert, Delete, Find, Traverse, Size
• Advantages can grow, delete/insert with
  assignments

2
Complexities

• Queue
• Insert O(1)
• Remove O(1)
• Peek O(1)
• isEmpty O(1)
• isFull O(1)
• List
• Insert O(1)
• Remove O(1)
• Search O(N)

• Stack
• Push O(1)
• Pop O(1)
• Peek O(1)
• isEmpty O(1)
• isFull O(1)

3
Stack Implementation

• With an array
• Need stack array and top members.
• Push (topltMAX) ? stacktop data lterrorgt
• Pop (topgt0) ? return stack--toplterrorgt
• With a linked list
• Push insert at front of list.
• Pop remove from front of list.
• What are the complexities?

4
Stack Array Implementation

• int top, arraySize Data array
• void Stack(int s)
• array malloc(sizeof(Data)s arraySize s
  top -1
• int push(Data s)
• if (isFull()) return false arraytop s
  return true
• Data pop() if (isEmpty()) return null
  return arraytop--
• int isEmpty() return (top lt 0)
• int isFull() return top1
  arraySize
• Data peek() if (isEmpty()) return null
  return arraytop

Note In C, non-zero true, zero false
5
Stack Linked List Implementation

• Data top
• Stack() top NULL
• void push(Data d) d-gtlinktop topd
• Data Pop()
• if (isEmpty()) return null Data
  value top top value-gtlink return value
  
• int isEmpty() return (top NULL)
• Data peek() return top

6
Queue Implementation

• With an array
• Circular Queue
• Need queue array, size, head, and tail pointers.
• Insert (sizeltMAX) ? queuetailMAX data
  lterrorgt
• Remove (size gt 0) ? return queueheadMAX
  lterrorgt
• With a linked list
• Insert Insert to back of queue
• Remove Remove from front of queue.
• What are the complexities?

7
Queue Array Implementation

• int head, tail, entries
• int size
• Data array public Queue(int s)
  array malloc(sizeof(Data)s) size s
  head 0 tail -1 entries 0
• public boolean insert(Data s) if
  (isFull()) return 0 if (tailsize) tail -1
• arraytail s entries return
  1
• public Data remove() if
  (isEmpty()) return NULL Data temp
  arrayhead head (head1)size
  entries-- return temp
• int isEmpty() return entries 0
  
• Data peek() if (isEmpty() return
  0 return
  arrayhead

8
Queue Linked List Implementation

• Data head, tail
• Queue(int s) head null tail
  null
• int Insert(Data s) if (isEmpty())
  head tail s else last-gtlink
  value tail s return true
• Data Remove() Data
  value head
• if (isEmpty()) return NULL
  head head-gtlink if (head NULL) tail
  NULL return value
• int isEmpty() return (head
  null
• Data peek() return head

9
Linked List ImplementationSee Text Example

• With dynamic memory
• The data structure uses object links.
• Insert/Delete Search assignments to change
  pointers
• With an array (Use indices instead of data links)
• Need to list array, size, and pointer to initial
  entry.
• Initialization Create free entry chain.
• Insert retrieve from free list if any and do
  normal insertion.
• Delete Do normal insertion logic and then add to
  free list.
• The data structure uses primitive links rather
  than object links.

10
Ordered Linked List Insertion

• Item first
• void insert(Item d )
• Item previous null Item current
  firstwhile (current!NULL d-gtkey gt
  current-gtkey) previouscurrent
  currentcurrent-gtnext)
• if (previous NULL) first d else
  previous-gtnext d
• d-gtnext current

Note Duplicates OK in this implementation
11
Linked List Removal

• Item remove(Item d)
• Item current first previous NULL
• do
• if (current null) return NULL
• if (!equals(current-gtkey, d-gtkey))
  
• previous current current
  current-gtnext while (current!null
  !equals(current-gtkey, d-gtkey))
• if (previous NULL) first
  first-gtnext else previous-gtnext
  current-gtnext
• return current

12
Doubly Linked ListSee Text Example

• Two links. One to next record and one to
  previous.
• Characteristics.
• More assignments to maintain links.
• Dont need the previous temporary pointer.
• More memory per record.
• More secure. Used for operating systems.

13
Doubly Linked Insertion

• void insert( Item d )
• Item current first, previous
  NULLwhile (current!NULLcompareTo(d-gtkey,
  current-gtkey)lt0)
• previous current currentcurrent-gtnext)
  
• if (current NULL) if (previous
  NULL) first current else previous-gtnext
  d
• else
• if (current-gtpreviousNULL)
• firstd d-gtnextcurrent
  current-gtpreviousd
• else d-gtprevious
  current-gtprevious d-gtnext current
• current-gtprevious-gtnext
  d current-gtprevious d

14
Doubly Linked Removal

• int remove(Item d)
• Item current first
• do
• if (current NULL) return NULL
• if (current-gtkey ! d-gtkey) current
  current-gtnext while (!equals(current-gtkey
  , d-gtkey))
• if (current-gtprevious NULL) first
  current-gtnext else current-gtprevious-gtnext
  current-gtnext
• if (current-gtnext ! NULL)
  current-gtnext-gtprevious current-gtprevious
• return true

15
Stack Examples

• Matching pairs of delimiters
• Evaluating infix expressions
• Two stacks
• First convert to postfix and then evaluate
• Expression examples
• ....lt...gt.....
• 500/(12(345/2))(321)