Stacks

Stacks are fundamental data structures that follow the Last-In-First-Out (LIFO) principle—like a stack of plates, you add to the top and remove from the top. This simple constraint makes stacks perfect for tracking history, managing nested structures, and reversing order.

Stacks appear everywhere in computer science: function call management, undo/redo functionality, parsing expressions, and depth-first search. In coding interviews, recognizing when to use a stack—usually when you need to match pairs, process elements in reverse, or track nested structures—is a valuable skill.

What You'll Learn

• Stack Basics: How stacks work, the core operations (push, pop, peek), implementation approaches using arrays or linked lists, and time complexity analysis. You'll understand when stacks are the right choice.

• Stack Operations: Working with stacks including checking for empty, getting size, and common patterns like using stacks for temporary storage, reversing sequences, and maintaining history.

• Stack Problems: Classic interview problems including valid parentheses, evaluate expressions, implement min stack, daily temperatures, and using stacks for depth-first search and backtracking.

Why It Matters

Stack problems are common in interviews because they test your understanding of data structure properties and pattern recognition. The key insight: whenever you see matching/nesting (parentheses, tags), or need to process "most recent first," think stacks.