A Stack is a data structure operating on the LIFO (Last In, First Out) principle, meaning the last element added to the stack is the first one to be removed. Imagine a stack of plates: you can only pick up the plate at the top.

Core Stack Operations

  1. push(x) — Adds element x to the top of the stack.
  2. pop() — Removes and returns the top element from the stack.
  3. peek() / top() — Views the top element without removing it.
  4. isEmpty() — Checks whether the stack is empty.
  5. size() — Returns the total number of elements in the stack.

Use Cases

Stacks are widely used in algorithms and software engineering:

  1. Reverse Order Evaluation: Performing computations in Reverse Polish Notation (RPN).
  2. Recursion: Managing function calls via the call stack.
  3. Undo Functionality: Implementing the "Undo" action in text editors and games.
  4. Parentheses Balancing: Checking the validity of bracket expressions.
  5. Graph Traversal: Implementing Depth-First Search (DFS).

Advantages of a Stack

  • Simplicity: Straightforward implementation.
  • High Performance: All basic operations execute in O(1) time complexity.

Disadvantages of a Stack

  • Restricted Access: You can only access the topmost element.
  • Size Limitations: Can be fixed in size if implemented using a static array.