Stacks and Basic Operations
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Questions and Answers

What is the first step in evaluating a postfix expression?

  • Create a stack to store operands. (correct)
  • Push the operators into the stack.
  • Scan the expression from right to left.
  • Output the final result immediately.

In postfix evaluation, operators are pushed onto the stack.

False (B)

What do you do at the end of a postfix evaluation?

Pop the final result from the stack.

In the expression '10 + 2 * 8 - 3', the postfix notation is __________.

<p>10 2 8 * + 3 -</p> Signup and view all the answers

Match the following components with their functions in postfix evaluation:

<p>Operand = Pushed onto the stack for storage Operator = Pops operands from the stack and evaluates Stack = Holds the operands during evaluation Expression End = Final result is in the stack</p> Signup and view all the answers

What is the correct operation to insert an element at the top of a stack implemented with a linked list?

<p>Push (A)</p> Signup and view all the answers

Popping from a stack removes the element at the end of the stack.

<p>False (B)</p> Signup and view all the answers

What data structure is utilized to implement a stack in the given content?

<p>Linked List</p> Signup and view all the answers

In a stack, the last element pushed is the first element ______.

<p>popped</p> Signup and view all the answers

Which of the following is NOT an application of stacks?

<p>Database management (B)</p> Signup and view all the answers

The first character pushed into the stack will be the last character popped out during string reversal.

<p>True (A)</p> Signup and view all the answers

What does the term 'top' refer to in the context of stack implementation using a linked list?

<p>The topmost node in the stack</p> Signup and view all the answers

Match the following stack operations with their descriptions:

<p>Push = Inserting an element at the top of the stack Pop = Removing an element from the top of the stack Peek = Retrieving the top element without removing it IsEmpty = Checking if the stack has no elements</p> Signup and view all the answers

What does LIFO stand for in the context of stacks?

<p>Last In, First Out (A)</p> Signup and view all the answers

In a stack, elements can be added and removed from both ends.

<p>False (B)</p> Signup and view all the answers

What is the purpose of the 'peek' operation in a stack?

<p>To examine the top element of the stack without removing it.</p> Signup and view all the answers

The operation to add an element to the stack is called __________.

<p>push</p> Signup and view all the answers

What happens to the 'top' variable in a stack when an element is pushed?

<p>It increases by one. (A)</p> Signup and view all the answers

In an array implementation of a stack, if the 'top' variable is -1, it indicates that the stack is empty.

<p>True (A)</p> Signup and view all the answers

What data structure is commonly used to implement a stack, and what is the maximum size specified in the given array implementation?

<p>Array, with a maximum size of 10.</p> Signup and view all the answers

What does FIFO stand for in the context of queues?

<p>First-In, First-Out (B)</p> Signup and view all the answers

In a queue, elements can be added at both ends.

<p>False (B)</p> Signup and view all the answers

What operation would you use to remove an element from the front of a queue?

<p>dequeue</p> Signup and view all the answers

The operation called ______ allows you to add an element to the back of a queue.

<p>enqueue</p> Signup and view all the answers

Match the following queue operations with their functions:

<p>enqueue = Add an element to the back dequeue = Remove the front element peek = Examine the front element isEmpty = Check if the queue has no elements</p> Signup and view all the answers

Which of the following is a common real-world example of a queue?

<p>People waiting in line at a bank (C)</p> Signup and view all the answers

A queue can utilize both arrays and linked lists for its implementation.

<p>True (A)</p> Signup and view all the answers

What would happen if you call the 'peek' operation on an empty queue?

<p>It returns null.</p> Signup and view all the answers

What happens to the 'rear' pointer when a new element is added to a queue implemented with a linked list?

<p>It points to the new element. (C)</p> Signup and view all the answers

What operation happens when an element is added to the queue?

<p>Enqueue (A)</p> Signup and view all the answers

A queue implemented with a linked list can run out of space.

<p>False (B)</p> Signup and view all the answers

The front of the queue is initialized to 0 when it is empty.

<p>False (B)</p> Signup and view all the answers

What does the dequeue operation do in a queue implemented using a linked list?

<p>It removes the element from the front of the queue.</p> Signup and view all the answers

The operation to view the front element of the queue without removing it is called __________.

<p>peek</p> Signup and view all the answers

What happens to the 'size' variable during an enqueue operation?

<p>It is incremented.</p> Signup and view all the answers

When an element leaves the queue, the variable 'first' is updated to the new __________.

<p>front</p> Signup and view all the answers

Match the queue operations with their descriptions:

<p>enqueue = Adding an element to the queue dequeue = Removing an element from the queue peek = Retrieving the front element without removing it queueIsFull = Checking if the queue is full</p> Signup and view all the answers

What condition indicates the queue is full?

<p>rear == MAXSIZE - 1 (D)</p> Signup and view all the answers

The dequeue operation does not change the rear of the queue if the front and rear are different.

<p>True (A)</p> Signup and view all the answers

What value does the peek operation return?

<p>The value at the front of the queue.</p> Signup and view all the answers

What is the main advantage of using a circular array for implementing a queue?

<p>It prevents wastage of array space by wrapping around. (B)</p> Signup and view all the answers

In a circular array implementation, the rear pointer can move to an index less than zero.

<p>False (B)</p> Signup and view all the answers

What value is assigned to the 'rear' pointer when the queue is initially empty?

<p>0</p> Signup and view all the answers

In the enqueue operation, if the queue is not full, the rear pointer is updated using the formula (rear + 1) % __________.

<p>MAXSIZE</p> Signup and view all the answers

Match the following operations with their expected results in a queue implemented with a circular array:

<p>enQueue = Add an element to the end of the queue deQueue = Remove an element from the front of the queue queueIsFull = Check if the queue has reached maximum capacity peek = View the element at the front without removing it</p> Signup and view all the answers

Which condition checks whether the queue is full in the queueIsFull function?

<p>((rear + 1) % MAXSIZE == front) (D)</p> Signup and view all the answers

The dequeue operation removes an element and adjusts the front pointer if the queue is empty.

<p>False (B)</p> Signup and view all the answers

What happens to both the front and rear pointers when the last element is dequeued?

<p>Both are set to -1</p> Signup and view all the answers

Flashcards

Postfix expression

A notation where operators follow their operands.

Infix expression

A notation where operators are placed between their operands.

Evaluating postfix expressions

A process to calculate a postfix expression using a stack. Numbers get pushed onto the stack. Operators pop two operands evaluate, and push the result back.

Stack in postfix evaluation

Used to temporarily hold operators and operands during postfix expression calculation.

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Postfix evaluation algorithm

Algorithm involving pushing numbers, popping them for operations, and pushing the result.

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Stack

A list where insertions and deletions happen at one end (top).

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Push operation

Adding an element to the top of a stack.

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Pop operation

Removing an element from the top of a stack.

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Peek operation

Looking at the element at the top of a stack without removing it.

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Stack implementation (array)

A stack stored in an array, offering efficient operations with fixed size.

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Stack implementation (linked list)

A stack stored in a linked list, allowing dynamic size.

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Empty stack

A stack with no elements.

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Top of stack

The element at the end (highest position) of the stack.

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Push Operation (Stack)

Adds an element to the top of the stack by inserting a new node at the beginning of the linked list.

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Pop Operation (Stack)

Removes and returns the element from the top of the stack by deleting the node at the beginning of the linked list.

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Stack Applications

Stacks are useful for tasks such as line editing, expression evaluation, managing function calls, and browser history.

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Reversing Strings

Pushing characters of a string onto a stack and then popping them to reverse the string.

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Infix to Postfix Conversion

Changing an expression written in infix notation to postfix notation, which is suitable for evaluation using a stack.

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Node Structure

A structure that represents an element in a linked list, containing data and a pointer to the next node in the list.

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Stack Overflow/Underflow

Stack Overflow is when trying to push an element onto a full stack, and Underflow occurs when trying to pop from an empty stack.

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What is a Queue?

A queue is a data structure like a line where elements are added at the back (enqueue) and removed from the front (dequeue). It follows the "First-In, First-Out" (FIFO) principle.

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Enqueue

Adding an element to the rear of the queue. It's like someone joining the back of a line.

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Dequeue

Removing an element from the front of the queue. It's like the first person in line leaving.

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Peek

Looking at the element at the front of the queue without removing it. Like checking who's next in line.

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Queue Implementation - Array

A queue can be implemented using an array. This means storing elements in consecutive memory locations. The array acts as a storage space.

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Queue Implementation - Linked List

A queue can be implemented using a linked list. Here, each element points to the next element in the queue. This allows dynamic sizing.

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Queue Motivation

Queues are used in various applications like operating systems (managing processes, print jobs, network packets), programming (modeling lines of customers, tasks to be executed), and real-world scenarios (escalator, cars at a gas station).

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Queue Implementation using a Linked List

A queue data structure can be implemented using a linked list, where the head (front) pointer points to the first element and the tail (rear) pointer points to the last element.

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enQueue Operation

Adding an element to the rear of the queue by creating a new node, setting its data to the given value, and updating the rear pointer to point to the new node.

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deQueue Operation

Removing and returning the element at the front of the queue. This involves updating the front pointer to point to the next element and deleting the old front node.

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Queue: Circular Array vs. Linked List

Both circular arrays and linked lists can be used to implement queues. Circular arrays are more efficient for space utilization, while linked lists are more flexible for dynamic resizing.

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Queue Implementation using Array

Using a fixed-size array to represent a queue. It involves keeping track of the front and rear indices, as well as the size of the queue.

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Circular Queue

A queue implementation using an array where the rear wraps around to the beginning of the array when reaching the end, effectively utilizing the entire array space.

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Queue Overflow

An attempt to enqueue an element into a full queue, causing an error.

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Queue Underflow

An attempt to dequeue an element from an empty queue, causing an error.

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Circular Array

A data structure where the end of the array wraps around to the beginning, allowing efficient management of queues.

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Queue Implementation using Circular Array: enqueue

Adds an element to the rear of the queue, using the circular array to handle overflow.

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Queue Implementation using Circular Array: dequeue

Removes an element from the front of the queue, using the circular array to handle underflow.

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Queue Implementation using Circular Array: isFull

Checks if the queue is full using the circular array, preventing overflow.

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Queue Implementation using an Array: Limitations

This implementation has a fixed capacity due to the fixed size of the array.

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Queue Implementation using an Array: Behaviour at Rear

When the rear reaches the end of the array, it needs special handling to prevent buffer overflow.

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Queue Implementation: Advantages and Disadvantages

Array implementation is simple but has a fixed size, while circular array implementation tackles overflow but may be more complex.

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Queue Implementation: Why Circular Array?

Circular arrays are efficient, providing a constant-time method for inserting and removing elements from the queue.

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Study Notes

Stacks

  • Stacks are lists with a specific restriction
  • Insertions and deletions happen at the same end, called the top of the stack.
  • Implements Last-In, First-Out (LIFO) method.
  • Elements are removed in the reverse order they were added.

Basic Stack Operations

  • push(add): Adds an element to the top of the stack.
  • pop(remove): Removes an element from the top of the stack.
  • peek(top): Retrieves the top element of the stack without removing it.
  • isEmpty: Checks if the stack is empty.
  • size: Determines the number of elements in the stack.

Stack Implementation

  • Using an Array: Efficient for implementing stacks, but has a fixed size.
    • MAXSIZE is the maximum size of the array.
    • top keeps track of the current top element. Intialized to -1.
  • Using a Linked List: No fixed size, can grow dynamically.

Stack Implementation (Example using array and operations)

  • Push Operation: Increases the top index by 1 and stores the new element at that location.
  • Pop Operation: Returns the value at the top index, then decreases the top index by 1.

Motivation - Stacks Applications

  • Line editing: Tracks undo and redo operations.
  • Reverse a string: Reverses a string using LIFO.
  • Matching brackets: Ensures proper order of brackets.
  • Postfix calculation: Evaluates expressions in postfix notation.
  • Function call stack: Manages function calls in programming.
  • Browsers: History and back/forward functions.

Reversing Strings

  • To reverse a string, characters are pushed onto the stack from left to right.
  • Popping them off the stack creates the reverse string order.

Infix to Postfix Conversion

  • Converts expressions from infix notation to postfix notation. This is necessary for stacks to evaluate the result of an expression.
    • Operands are printed as they are encountered.
    • Parentheses control operator order.
    • Operators with higher precedence are pushed before lower precedence ones.

Evaluating Postfix Expressions

  • A stack-based approach is utilized to calculate the output of a postfix expression.
    • If the token is an operand, push onto the stack.
    • If the token is an operator, pop the top two operands from the stack, apply the operator to them, push the result onto the stack.

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Related Documents

Lecture 3 - Queues PDF
Lecture 4 - Stacks PDF

Description

This quiz explores the concept of stacks, including their structure and operations. You will learn about push, pop, peek, and checks for emptiness and size. Additionally, it covers stack implementation using arrays and linked lists.

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