Data Structures and Algorithms: Stacks

Questions and Answers

What is the primary characteristic of a stack data structure?

It is a fixed-size structure

It is a random access structure

It is a last-in, first-out (LIFO) structure (correct)

It is a first-in, first-out (FIFO) structure

In a stack, where do addition and deletion of elements occur?

At the middle of the stack

At the beginning of the stack

At the end of the stack, also called the top (correct)

At random locations in the stack

Which of the following is an example of a stack application?

Performing matrix operations

Evaluating balanced symbols in compilers (correct)

Managing a queue of customers

Storing a large amount of data

How can a stack be implemented in C++?

Using either an array or a linked list Signup and view all the answers

What is the primary advantage of using a linked list to implement a stack?

It provides more flexibility in terms of dynamic memory allocation Signup and view all the answers

What is the purpose of the undo operation in text editors, which is implemented using a stack?

To keep track of all text changes Signup and view all the answers

In a stack-based implementation, which operation is typically more efficient?

Insertion at the top of the stack Signup and view all the answers

What is the primary advantage of using a stack to remove recursion?

It avoids the risk of stack overflow Signup and view all the answers

What is the time complexity of removing an element from the head of a linked list-based stack?

O(1) Signup and view all the answers

Which of the following is a characteristic of a linked list-based stack implementation?

Dynamic memory allocation Signup and view all the answers

What is the purpose of the initializeStack function in a linked list-based stack implementation?

To deallocate memory occupied by the stack elements Signup and view all the answers

What is the purpose of the push function in a linked list-based stack implementation?

To add a new element at the beginning of the linked list Signup and view all the answers

Which of the following is a benefit of using a linked list-based stack implementation?

Dynamic memory allocation Signup and view all the answers

What is the purpose of the pop function in a linked list-based stack implementation?

To remove the top element from the stack Signup and view all the answers

What is the time complexity of pushing an element onto a linked list-based stack?

O(1) Signup and view all the answers

What is the purpose of the top function in a linked list-based stack implementation?

To return the information of the node to which stackTop is pointing Signup and view all the answers

What is the purpose of the isFullStack function in a linked list-based stack implementation?

Always returns false Signup and view all the answers

What is the primary purpose of the isFullStack operation in a stack?

To check if the stack is full Signup and view all the answers

What is a characteristic of a dynamic stack implemented as a linked list?

It grows in size as needed Signup and view all the answers

Which of the following is an application of stacks?

Printing a linked list backward Signup and view all the answers

What is the purpose of the stackTop variable in an array-based stack implementation?

To point to the top of the stack Signup and view all the answers

What is the precondition for the pop operation in a stack?

The stack must exist and must not be empty Signup and view all the answers

What is the purpose of the initializeStack operation in a stack?

To initialize the stack to an empty state Signup and view all the answers

What is the primary purpose of the top operation in a stack?

To retrieve the top element of the stack without removing it Signup and view all the answers

What is the benefit of using a linked list to implement a stack?

It can grow in size as needed Signup and view all the answers

What is the primary purpose of the push operation in a stack?

To add a new element onto the stack Signup and view all the answers

What is the purpose of the isEmptyStack operation in a stack?

To check if the stack is empty Signup and view all the answers

What is the purpose of the stackADT class in a stack implementation?

To define the stack operations as an abstract data type Signup and view all the answers

Study Notes

Stack Concept

A stack is a data structure similar to arrays and linked lists, holding a sequence of elements.
It follows the Last-In, First-Out (LIFO) principle, meaning addition and deletion of elements occur only at one end, called the top.

Real-Life Examples of Stacks

A bookshelf is a real-life example of a stack, where you need to remove the first book to access the one behind it.

Stack Applications

Evaluating balanced symbols in compilers to check for syntax errors.
Undo operation in text editors, where all text changes are stored in a stack.
Parsing arithmetic expressions, such as ((24-6/3)(3*5+8/4))-(2+3).

Stack Abstract Data Type (ADT)

The class stackADT defines stack operations as an Abstract Data Type (ADT).
It includes operations such as push, top, pop, isFullStack, isEmptyStack, and initializeStack.

Stack Operations

Push: adds a new element onto the stack, with a precondition that the stack must exist and not be full.
Top: retrieves the top element of the stack without removing it, with a precondition that the stack must exist and not be empty.
Pop: removes the top element from the stack, with a precondition that the stack must exist and not be empty.
IsFullStack: checks if the stack is full and returns true or false.
IsEmptyStack: checks if the stack is empty and returns true or false.
InitializeStack: initializes the stack to an empty state.

Implementing Stack ADT

A stack can be implemented as either an array or a linked list structure.
Stacks implemented as arrays are static, having a fixed size, while those implemented as linked lists are dynamic, growing in size as needed.

Implementing Stack using Array

The first stack element is put in the first array slot, the second in the second slot, and so on.
The top of the stack is accessed through the index of the last element added to the stack.
A variable (stackTop) is used to keep track of the top position of the array.

Implementing Stack using Linked List

A linked list implementation of a stack is more efficient for inserting and removing elements at the head.
The default constructor initializes the stack to an empty state by setting stackTop to NULL.
The stack is never full, as memory is allocated and deallocated dynamically.
The isFullStack function always returns false.

Stack Operations using Linked List

Push: adds a new element at the beginning of the linked list, updating the stackTop pointer.
Pop: removes the top element of the stack, updating the stackTop pointer.
Top: returns the information of the node pointed to by stackTop.

Removing Recursion

A stack can be used to design a non-recursive algorithm to print a linked list backward.
A non-recursive algorithm can be used to print a linked list backward using a stack.

STL Class Stack

The Standard Template Library (STL) provides a class to implement a stack in a program.
The STL class stack is similar to the implementation described in the Textbook.

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Description

Learn about stacks and their operations, including implementation as an array and linked list. Part of the Data Structures and Algorithms course, Semester 2, 2023/2024.