When learning about data structures, one of the simplest yet most powerful concepts is the stack. Just like its real-world counterpart—a stack of plates in your kitchen—this structure follows a very specific order for adding and removing items. Let’s dive deeper into what stacks are, why we need them, and where they shine in real-world applications.

What is a Stack?

A stack is a linear data structure that follows the LIFO (Last In, First Out) principle.

  • Last In → The last element added to the stack will be the first one removed.
  • First Out → The element added earliest will only be removed once everything added after it is removed.

Think of it as a pile of books—if you put a book on top, it’s the first one you’ll remove.

Stacks typically support two main operations:

  • Push → Add an element to the top.
  • Pop → Remove the element from the top.

Why Do We Need Stacks?

Stacks are crucial because they help us manage data in an order-dependent way. Their restricted operations make them predictable and efficient for solving problems where order of processing matters. Some common reasons we need stacks:

  • Managing function calls in programming (call stack).
  • Undo/redo functionality in applications.
  • Parsing expressions and checking balanced parentheses.
  • Backtracking algorithms (mazes, puzzles, etc.).

When Should We Use a Stack?

You should use a stack when:

  • You need to process elements in reverse order of their arrival.
  • You want a controlled way to temporarily store items.
  • You need fast insertion and removal at one end only.

If your use case involves removing items in the same order they were added, a queue (FIFO) might be more suitable.

A Real-World Example

Consider the browser back button.

  • Each time you visit a new page, the URL is pushed onto a stack.
  • When you press the back button, the last visited page is popped off, and the browser takes you to the previous one.

This is a perfect example of LIFO behavior in everyday life.

Time and Memory Complexities

Stacks are highly efficient since most operations occur at the top of the structure:

  • Pushing (insertion): O(1) – constant time.
  • Popping (deletion): O(1) – constant time.
  • Peeking (viewing top element): O(1) – constant time.
  • Memory complexity: O(n) – proportional to the number of elements stored.

This makes stacks a great fit when you need quick and predictable operations.

Final Thoughts

Stacks may sound simple, but they form the foundation of many critical systems in computer science. From managing program execution to enabling undo features in your favorite text editor, stacks are everywhere. Mastering them is a big step in becoming a stronger programmer.