Stack Data Structure

A stack is a linear data structure that follows the LIFO (Last In, First Out) principle. This means that the element inserted last is the first one to be removed.

A simple real-life analogy is a stack of plates:

  • You place a new plate on top
  • You also remove plates from the top

Thus, insertion and deletion both occur at the same end, called the top.

Applications of Stack

Stacks are widely used in computer science due to their simplicity and efficiency in handling specific types of problems.

Common Uses

  • Reversing data (strings, numbers)
  • Managing function calls (recursion)
  • Expression evaluation (infix, postfix, prefix)
  • Syntax parsing (compilers)
  • Backtracking algorithms
  • Browser history navigation (back/forward)

Stack Terminology

Understanding basic terms is essential for designing and implementing stack-based algorithms.

Top

  • Represents the most recently added element
  • Indicates the current position of the stack

Push

  • Operation of adding an element to the stack
  • Element is inserted at the top

Pop

  • Operation of removing the top element
  • Reduces the size of the stack

Underflow

  • Occurs when trying to pop from an empty stack

Overflow

  • Occurs when trying to push into a full stack (in fixed-size stacks)

LIFO (Last In, First Out)

  • Principle followed by stack

Stack Pointer

  • Variable that keeps track of the top element

Working of Stack

A stack operates in a restricted manner where:

  • Insertion (push) happens only at the top
  • Deletion (pop) also happens only from the top
  • There is only one entry and exit point

Step-by-Step Working

Consider a stack of size 5:

  • Initially, the stack is empty
  • Elements are inserted one by one using push:
    • Push 1 → Stack: [1]
    • Push 2 → Stack: [1, 2]
    • Push 3 → Stack: [1, 2, 3]
    • Push 4 → Stack: [1, 2, 3, 4]
    • Push 5 → Stack: [1, 2, 3, 4, 5]

Now the stack is full (overflow condition if we push more)

Deletion Process

  • Pop removes elements in reverse order:
    • Pop → removes 5
    • Pop → removes 4
    • Pop → removes 3

This clearly shows LIFO behavior.

Standard Stack Operations

Coming up next are some basic activities actualised on the stack:

  • push(): When we embed a component in a stack then the activity is known as a push. On the off chance that the stack is full, at that point the flood condition happens.
  • pop(): When we erase a component from the stack, the activity is known as a pop. In the event that the stack is unfilled implies that no component exists in the stack, this state is known as an undercurrent state.
  • isEmpty(): It decides if the stack is unfilled or not.
  • isFull(): It decides if the stack is full or not.'
  • peek(): It restores the component at the given position.
  • display(): It prints all the components accessible in the stack.

Real-World Examples of Stack

Stacks are used in many real-world applications:

Undo/Redo operations: Text editors store actions in a stack

Browser History : Back and forward navigation

Function Call Management: Each function call is stored in the call stack

Expression Evaluation: Used in calculators and compilers

Parentheses Matching: Checking balanced expressions

Advantages of Stack

  • Simple and easy to implement
  • Efficient for LIFO-based problems
  • Useful in recursion and backtracking

Limitations of Stack

  • Limited access (only top element accessible)
  • Fixed size may cause overflow (in array implementation)
  • Not suitable for random access

Conclusion

The stack is a fundamental data structure that plays a crucial role in many areas of computer science.

  • Follows LIFO principle
  • Supports efficient insertion and deletion
  • Widely used in algorithms, compilers, and system design

Mastering stacks is essential for solving many real-world and competitive programming problems.