Learn Stack Data Structure- Revision Notes

Introduction to Stack Data Structure

A stack is a linear data structure that follows the Last In, First Out (LIFO) principle. The most recently added element is the first to be removed. A real-life example of a stack is a stack of plates in a cafeteria; you can only take the top plate, and you add new plates on the top.

Importance and Applications of Stack Data Structure

→ Function Call Management: Stacks are used to manage function calls in programming languages.
Example: When you call a function in a programming language, it gets added to the call stack. If that function calls another function, it also gets added to the stack, and so on. Once a function completes, it is removed from the stack. This stack-based management ensures that functions return control to the correct place in the code.

→ Undo Mechanisms: Many software applications use stacks to implement undo features.
Example: In text editors like Microsoft Word, every action you perform (like typing a letter or deleting a word) is pushed onto a stack. When you press "undo," the last action is popped from the stack and reversed.

→ Expression Evaluation: Stacks are used in parsing expressions and evaluating postfix expressions.
Example: In calculators and interpreters, stacks are used to evaluate postfix (Reverse Polish Notation) expressions efficiently. For instance, the expression "3 4 + 2 *" can be evaluated using a stack by pushing and popping operands and operators.

→ Syntax Parsing: Compilers use stacks for syntax parsing and checking the correctness of code.
Example: During the compilation process, a compiler uses a stack to parse and ensure that code syntax is correct. For instance, it checks that every opening bracket has a corresponding closing bracket, helping to identify syntax errors.

Key Operations of Stack Data Structure

→ Push: Add an element to the top of the stack.
→ Pop: Remove the top element from the stack.
→ Peek: View the top element without removing it.
→ isEmpty: Check if the stack is empty.
→ isFull: Check if the stack is full (for fixed-size stacks).

Push Operation in Stack Data Structure

The push operation adds an element to the top of the stack. Here's the algorithm and pseudocode:

Algorithm:

1. Check if the stack is full.
2. If the stack is full, throw an overflow error.
3. If the stack is not full, add the element to the top of the stack.
4. Increment the top pointer.

Pseudocode:

function push(stack, element):
    if stack is full:
        throw overflow error
    else:
        stack[top] = element
        top = top + 1
    

Pop Operation in Stack Data Structure

The pop operation removes the top element from the stack. Here's the algorithm and pseudocode:

Algorithm:

1. Check if the stack is empty.
2. If the stack is empty, throw an underflow error.
3. If the stack is not empty, remove the top element from the stack.
4. Decrement the top pointer.

Pseudocode:

function pop(stack):
    if stack is empty:
        throw underflow error
    else:
        top = top - 1
        return stack[top]
    

Peek Operation in Stack Data Structure

The peek operation returns the top element of the stack without removing it. Here's the algorithm and pseudocode:

Algorithm:

1. Check if the stack is empty.
2. If the stack is empty, throw an underflow error.
3. If the stack is not empty, return the top element of the stack.

Pseudocode:

function peek(stack):
    if stack is empty:
        throw underflow error
    else:
        return stack[top - 1]
    

isEmpty Operation in Stack Data Structure

The isEmpty operation checks if the stack is empty. Here's the algorithm and pseudocode:

Algorithm:

1. Check if the top pointer is at the initial position.
2. If the top pointer is at the initial position, return true.
3. Otherwise, return false.

Pseudocode:

function isEmpty(stack):
    if top == 0:
        return true
    else:
        return false
    

isFull Operation in Stack Data Structure

The isFull operation checks if the stack is full. Here's the algorithm and pseudocode:

Algorithm:

1. Check if the top pointer is at the maximum capacity.
2. If the top pointer is at the maximum capacity, return true.
3. Otherwise, return false.

Pseudocode:

function isFull(stack):
    if top == stack.size:
        return true
    else:
        return false
    

Time Complexity and Space Complexity

Time Complexity: For push, pop, and peek operations, the time complexity is O(1) because these operations are performed in constant time.

Space Complexity: The space complexity is O(n), where n is the number of elements in the stack, due to the storage of elements in the stack.

Advantages of Stack Data Structure

→ Simple Implementation: Easy to implement and use.
→ Efficient Memory Management: Dynamically managed in linked list implementation.
→ Supports Recursion: Natural fit for recursive algorithms and function call management.

Disadvantages of Stack Data Structure

→ Limited Size: Array-based stack has a fixed size, leading to potential overflow.
→ No Random Access: Can only access the top element, making it inefficient for certain applications.
→ Overflow and Underflow: Prone to overflow and underflow errors.