Stack & Queue – AP CSA | ShowMeClass

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Stack & Queue

AP CSA · Unit 10: Recursion & Data Structures

Learning Objectives

Understand LIFO (Stack) vs FIFO (Queue) ordering

Perform push/pop on stacks, enqueue/dequeue on queues

Identify real-world applications of each

Know that all operations are O(1)

Stack (LIFO)

Last In, First Out
Think: stack of plates, undo history, call stack
push() — add to top
pop() — remove from top
peek() — view top

Queue (FIFO)

First In, First Out
Think: line at a store, print jobs, BFS
enqueue() — add to back
dequeue() — remove from front
peek() — view front

StackQueueLIFOFIFOO(1)

Stack (LIFO)

Queue (FIFO)

Stack Size

0

Stack Top

—

Queue Size

0

Queue Front

—

Operations

0

Value

Stack Operations

Queue Operations

Quick Fill

Operation Log

Quick Quiz▼

1. If you push 1, 2, 3 onto a stack and pop once, you get:

1 2 3 Error

2. If you enqueue A, B, C and dequeue once, you get:

A B C Error

3. Both push and enqueue are:

O(n) O(1) O(log n) O(n²)