👶Explain Like I'm 5
Imagine a stack of plates in your kitchen...
When you wash a plate, you put it on TOP of the stack. When you need a plate, you take the TOP one (the last one you added). You can't take a plate from the middle or bottom without removing the ones on top first!
Why is this useful? Stacks help us remember where we came from. Like browser back button, undo in editors, or checking if brackets are balanced!
Real-world use cases:
- Browser back/forward buttons
- Undo/Redo in text editors
- Function call stack in programming
- Balanced parentheses checking
- Expression evaluation
Interactive Stack Visualization
🎯 Stack: Last In, First Out (LIFO)
BOTTOM ⬇️
Stack is empty 📭
Size
0
Top Element
N/A
Is Empty?
Yes
Stack Operations
⬆️PUSH(x)
Add element to the TOP of stack. O(1) time complexity.
⬇️POP()
Remove and return TOP element. O(1) time complexity.
👀PEEK() / TOP()
View TOP element without removing it. O(1) time complexity.
❓isEmpty()
Check if stack is empty. O(1) time complexity.
🎯When to Use Stack?
✅
Keywords: “reverse”, “undo”, “backtrack”, “nested”, “balanced”
✅
Need to: Process items in reverse order or remember previous states
✅
Problems: Parentheses matching, expression evaluation, DFS, backtracking
💡
Pro Tip: If you need “most recent” or “last added”, think Stack!