Stacks are an important part of computer science.

They are a type of linear data structure.

Stacks follow a rule called Last In, First Out (LIFO).

This means that the last item added to the stack is the first one to be taken out.

This rule makes stacks helpful for different tasks like:

• Managing function calls
• Reversing data
• Undoing actions in apps

Key Features of Stacks:

• LIFO Rule: The last item added is the first one removed.
• Basic Actions:
  • Push: Adds an item to the top of the stack.
  • Pop: Takes the top item off the stack.
  • Peek/Top: Shows the top item without taking it off.
• Size: The number of items in a stack is often noted as ( n ).

How Fast Are These Actions?

• Push: ( O(1) ) — This takes a constant amount of time since you’re just adding an item.
• Pop: ( O(1) ) — This also takes a constant amount of time because you’re just removing the top item.
• Peek: ( O(1) ) — This retrieves the top item without changing the stack.

How Are Stacks Made?

1. Array-based Stack: Uses a set-size array.
   • Benefits: Easy to use and fast.
   • Drawbacks: It has a fixed size, so it can't grow beyond this limit.
2. Linked List-based Stack: Uses flexible nodes that can grow as needed.
   • Benefits: The size can change, so it adapts easily.
   • Drawbacks: Takes up more memory because of the extra pointers.

Where Are Stacks Used?

• Managing Function Calls: Stacks keep track of the order of function calls and local variables. This is really important for when functions call each other (recursion).

• Evaluating Expressions: Stacks help in breaking down and calculating expressions in programming.

• Undo Features: Many applications use stacks to remember what users have done and let them go back to previous steps.

By learning about stacks and how they work in linear data structures, students can use them for solving problems in computing. This knowledge is important for understanding data structures and their real-life uses in computer science.