Stacks —
LIFO made crystal clear.
Last in, first out. It sounds simple — but stacks power function calls, undo systems, expression evaluation, and backtracking algorithms. Watch every push and pop animate in real time and stop losing track of what's on top.
What is a Stack?
A stack is a Last-In, First-Out (LIFO) data structure. The last element you push in is the first one to come out — like a stack of plates. Stacks are everywhere in computer science: function call management, undo operations, expression evaluation, and backtracking algorithms all rely on them.
Why visualization helps
Stack problems trip up beginners because it's hard to mentally track what's on top after several operations. LearnBug shows you the full stack state at every single step — elements push in from the top, pop out from the top, and the visual tower updates instantly.
Every stack operation, animated
From basic push/pop to interview-critical patterns — see each one execute live.
How the Call Stack Works
Every function call pushes a frame. Every return pops one. Watch Python's actual call stack build and unwind as your functions execute.
Balanced Parentheses
The classic stack interview problem. Watch opening brackets push and closing brackets pop — and see exactly when a mismatch is detected.
Reverse String with Stack
Push every character in, pop them out in reverse. A simple but powerful demonstration of LIFO — great entry point to stack thinking.
Infix to Postfix
Expression parsing with operator precedence. Watch operators push and pop based on priority as the postfix result builds up.
Next Greater Element
Monotonic stack in action. Watch elements wait on the stack until a larger element arrives to resolve them — O(n) elegance visualized.
Min Stack
Get the minimum element in O(1) at any time — even after pops. The auxiliary stack trick explained visually.
Run your stack code on LearnBug
Paste your code — bugs and all. See exactly what's on top at every step.