Lists, Queues, Stacks

CST200 – Week 5: Array based Implementation

Instructor: Andreea Molnar

Outline

•Lists

•Queues

•Stacks

ListA sequence of items that has at least the functionality below:

•Accessing an item at a given position

•Adding an item at a given position

•Removing an item

•Determining the number of items

StackA sequence of items in which:

•An item can be inserted only to the top

•Only the top item can be accessed/removed

In a stack items are inserted and removed according to the last-in first-out (LIFO) principle.

Stack

Functionality:

• push: insert an item to the top of the stack

• pop: remove the item at the top of the stack

• peek: get the item at the top of the stack

• isEmpty: assess if the stack is empty

• isFull: assess if the stack is full

Stack

Assuming that one has an object myStack:

myStack.push (25) 25 myStack

Stack

Assuming that one has an object myStack:

myStack.push (25)

myStack.push (10)10

25

myStack

StackAssuming that one has an object myStack:

myStack.push (25)

myStack.push (10)

int topValue = myStack.pop ()

10

25myStack

10 topValue

StackAssuming that one has an object myStack:

myStack.push (25)

myStack.push (10)

int topValue = myStack.pop ()

myStack.push (5)

5

25myStack

10 topValue

StackAssuming that one has an object myStack

myStack.push (25)

myStack.push (10)

int topValue = myStack.pop ()

myStack.push (5)

5

25myStack

10 topValue

StackAssuming that one has an object myStack:

myStack.push (25)

myStack.push (10)

int topValue = myStack.pop ()

myStack.push (5)

myStack.push (20)

20

5

25

myStack

10 topValue

StackAssuming that one has an object myStack:

myStack.push (25)

myStack.push (10)

int topValue = myStack.pop ()

myStack.push (5)

myStack.push (20)

topValue = myStack.pop ()

20

5

25

myStack

20 topValue

Queue

A sequence of items in which the first element inserted is the first one to be removed.

In a queue elements are inserted and removed based on the the first-in first-out (FIFO) principle.

Queue

Functionality:

• enqueue: add an item to the back of the queue

• dequeue: remove the front item

• getFront: get the front item

Queue

Assuming that one has an object myQueue:

myQueue.enque (25) 25 myQueue

Queue

Assuming that one has an object myQueue:

myQueue.enque (25)

int value = myQueue.deque () 25 myQueue

25 value

Queue

Assuming that one has an object myQueue:

myQueue.enque (25)

int value = myQueue.deque ()

myQueue.enque (20)

20 myQueue

25 value

QueueAssuming that one has an object myQueue:

myQueue.enque (25)

int value = myQueue.deque ()

myQueue.enque (20)

myQueue.enque (5)

20 5 myQueue

25 value

Queue

Assuming that one has an object myQueue:

myQueue.enque (25)

int value = myQueue.deque ()

myQueue.enque (20)

myQueue.enque (5)

value = myQueue.deque ()

20 5 myQueue

20 value

Summary

• A list is sequence of items that allows to access, add and remove an arbitrary element and determine the numbers of items (length/size of the list).

• A stack is a data structure in which an item can be added, accessed or removed only from the top.

• A queue is a data structure in which the first element added is the first one to be accessed/removed.