Data Structures: Stacks Overview

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Questions and Answers

What is the final result after evaluating the Postfix expression '7 4 -3 * 1 5 + / *'?

-2

-14 (correct)

-12

When evaluating an operator in a Postfix expression, what must be done first?

The operator should be pushed onto the stack.

Evaluate the operator without operands.

All operands should be stored in an array.

Operands must be popped from the stack. (correct)

In the expression '10 + 2 * 8 - 3', what will be the first output when converting to Postfix notation?

10 (correct)

What is the purpose of popping all operators from the stack at the end of the Postfix conversion?

To ensure no operators are left in the stack. Signup and view all the answers

Which step is NOT part of evaluating a Postfix expression?

Pushing operators onto the stack after evaluation. Signup and view all the answers

What does LIFO stand for in relation to stack operations?

Last-In, First-Out Signup and view all the answers

Which operation would you use to check the element at the top of the stack without removing it?

top Signup and view all the answers

What condition must be met to successfully execute a push operation on a stack implemented with an array?

top must be less than MAXSIZE Signup and view all the answers

What would the value of top be after popping an element from a stack where top was initially 3?

2 Signup and view all the answers

What will isEmpty return if the stack is initialized but has not had any elements pushed onto it?

true Signup and view all the answers

Which of the following is NOT a basic operation available for stack data structures?

insert Signup and view all the answers

In array implementation of a stack, what value should 'top' be initialized to?

-1 Signup and view all the answers

What happens if you try to pop from an empty stack using the described pop operation?

It throws an error Signup and view all the answers

What is the first action taken when encountering an operand during infix to postfix conversion?

Print it to the result. Signup and view all the answers

What should be done when a right parenthesis ')' is encountered?

Pop and print the top operator until the corresponding left parenthesis is found. Signup and view all the answers

When an operator is read, what is the initial check regarding the stack?

If the operator has higher or equal precedence compared to the stack's top. Signup and view all the answers

In the expression (A+B)*(C-D), which operation occurs when encountering the left parenthesis '('?

Push it into the stack. Signup and view all the answers

In the example expression 10 + 2 * 8 - 3, what happens after the operator '+' is read?

It is pushed to the stack. Signup and view all the answers

What is the result of the expression (A+B)*(C-D) in postfix notation?

AB+CD-* Signup and view all the answers

What occurs when the operator '-' is read in the expression 10 + 2 * 8 - 3?

Operators are popped from the stack until the '-' can be placed. Signup and view all the answers

In the sequence of operations during infix to postfix conversion, how are operators handled in relation to their precedence?

Higher or equal precedence operators are popped from the stack first. Signup and view all the answers

What is the primary function of the 'push' operation in a stack implemented with a linked list?

To insert an element at the beginning of the linked list Signup and view all the answers

What happens during the 'pop' operation in a stack using a linked list?

The element at the top is removed and returned Signup and view all the answers

In the context of a stack implemented as a linked list, what does it mean to 'push' elements into the stack?

To add elements into the stack in the last-in-first-out manner Signup and view all the answers

Which of the following applications is not typically associated with stacks?

Sorting an array Signup and view all the answers

When reversing the string 'a b c d e f' using a stack, which sequence applies to the 'pop' operation?

f e d c b a Signup and view all the answers

What is the purpose of maintaining a pointer called 'top' in a linked list stack implementation?

To maintain the head of the linked list Signup and view all the answers

Which of these represents a correct part of the 'push' implementation?

newNode->next = top; Signup and view all the answers

Why is a singly-linked list suitable for implementing a stack?

It efficiently manages memory by allowing dynamic size Signup and view all the answers

Study Notes

Stacks

Stacks are lists with a restriction: insertions and deletions are both performed at the same end, known as the top of the stack.
Stacks follow the Last-In, First-Out (LIFO) principle. The last item added is the first one removed.
Operations on a stack include:
- push (add): Adds an element to the top of the stack.
- pop (remove): Removes the element at the top of the stack and returns it.
- peek (top): Returns the element at the top of the stack without removing it.
- isEmpty: Checks if the stack is empty.
- size: Returns the number of elements in the stack.

Stack Implementations

Stacks can be implemented using arrays or linked lists.

Array Implementation

Using an array to store the stack elements.
Requires defining a MAXSIZE for the array's capacity.
A top variable tracks the index of the top element.
top is initialized to -1.

Linked List Implementation

Using a linked list to store the stack elements.
Each element in the list (node) stores a data value and a pointer to the next node.
The top pointer points to the first node in the list (the top of the stack).
top is initially NULL.

Stack Applications

Reversing Strings: Puts characters into a stack, then pops out in reverse order.
Bracket Matching: Stacks help check whether opening and closing brackets are matched correctly in a given expression.
Postfix Evaluation: Stacks are used to evaluate mathematical expressions in postfix notation.
Function Call Stack: Keeps track of function calls in computer programs (like a web browser's history).
Line Editing: Stacks are used to store characters during text editing, and can undo/redo changes.

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Description

Explore the concept of stacks in data structures, focusing on their unique Last-In, First-Out (LIFO) principle. This quiz will cover stack operations, implementations using arrays and linked lists, and key characteristics. Test your understanding of how stacks function and their practical applications.