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Sreekar Reddy
Sreekar Reddy

Posted on • Originally published at sreekarreddy.com

🎢 Queues Explained Like You're 5

A line at an amusement park

Day 39 of 149

👉 Full deep-dive with code examples


The Amusement Park Line

You're in line for a roller coaster:

[Exit] ← Person 1 ← Person 2 ← Person 3 ← [Entrance]
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First person in line → First to ride!

First In, First Out = FIFO


Queue Operations

  • Enqueue: Join the back of the line
  • Dequeue: Leave from the front
Enqueue "A" → [A]
Enqueue "B" → [A, B]
Enqueue "C" → [A, B, C]
Dequeue     → [B, C] (returns A)
Dequeue     → [C] (returns B)
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Fair! First come, first served.


Stack vs Queue

Stack (Pancakes) Queue (Line)
Last in, first out First in, first out
Add/remove from top Add at back, remove from front
Undo button Waiting line

Real Uses

  • 📨 Email inbox (process oldest first)
  • 🖨️ Print queue (print in order received)
  • 🎮 Server requests (handle in order)

In One Sentence

Queues process data in order received, like a fair line where the first person in is the first served.


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