Courses DSA Foundations

Stack & Queue Basics

Lessons: 8
Exercises: 49
Minutes: 49

1
Stacks
A last-in, first-out structure: push to the top, pop from the top.
Complete codeDebugCode orderMultiple choiceTapTrace
6 exercises
6 min
2
Queues
A first-in, first-out structure: add at the back, remove from the front.
Complete codeDebugFill blankMultiple choiceTapTrace
6 exercises
6 min
3
Stacks & Queues CheckpointCheckpoint
Prove you know LIFO vs FIFO and their operations before moving on to trees.
Complete codeDebugCode orderFill blankMultiple choiceTapTrace
7 exercises
8 min
4
Valid Parentheses
A stack remembers the most recent unclosed opener — every closer must match the top.
Complete codeMultiple choiceTapTrace
5 exercises
5 min
5
Min Stack
Store the min-so-far alongside each element so popping never loses the minimum's history.
Complete codeMultiple choiceTapTrace
5 exercises
5 min
6
Queue from Two Stacks
Two reversals restore original order — refill the out-stack only when it's empty.
Complete codeMultiple choiceTapTrace
6 exercises
5 min
7
Stack & Queue ReviewReview
Revisit the island's big ideas: LIFO vs FIFO, matching brackets with a stack, min-so-far pairs, and the two-stack queue.
DebugCode orderFill blankMultiple choiceTapTrace
6 exercises
6 min
8
Boss: Valid ParenthesesBoss
Solve Valid Parentheses end to end: choose the pattern, assemble the check, trace it, and handle every edge case.
Complete codeCode orderMultiple choiceTrace
8 exercises
8 min