🦥Recursion For Dummies

Hello friends!

Welcome to this week’s Sloth Bytes!

I hope you had a great week.

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Sloths have small brains.

HOWEVER, scientists are now realizing that this actually doesn’t relate to intelligence at all.

The brains of sloths might be small but they are very much focused on the specific skills that they need for survival.

Recursion: It's Not as Scary as You Think

Ever been told "just use recursion" and felt your brain melt? Let me simplify this concept with some simple examples.

What is Recursion?

Think of it like those Russian nesting dolls:

• Each doll contains a smaller version of itself

• Until you reach the smallest doll

• That's it. That's recursion.

For programming recursion is a function that calls itself until it shouldn't.

Why Use It?

Perfect for problems that:

• Have repeated smaller sub-problems

• Follow a pattern

• Deal with trees or nested structures

• Need to traverse directories

The 2 Steps of Recursion

Every recursive function needs:

1. A base case (when to stop)

2. A recursive case (when to continue)

That's all! It’s that simple.

Example

Calculating a factorial (5! = 5 × 4 × 3 × 2 × 1)

// ❌ Without recursion (iterative)
function factorial(n) {
  let result = 1;
  for(let i = n; i > 0; i--) {
    result *= i;
  }
  return result;
}

// ✅ With recursion (cleaner!)
function factorial(n) {
  // Base case: stop at 1
  if (n === 1) return 1;
  // Recursive case: n * factorial of (n-1)
  return n * factorial(n - 1);
}

What’s happening?

factorial(5) breaks down like this:

factorial(5)
→ 5 * factorial(4)
  → 4 * factorial(3)
    → 3 * factorial(2)
      → 2 * factorial(1)
        → 1 // We hit our Base case! Let's go back and add it up.
      ← 2 * 1 = 2 // 2 * factorial(1), factorial(1) = 1
    ← 3 * 2 = 6 // 3 * factorial(2), factorial(2) = 2
  ← 4 * 6 = 24 // 4 * factorial(3), factorial(3) = 6
← 5 * 24 = 120 // 5 * factorial(4), factorial(4) = 24

Common Use Cases

1. Directory traversal

   • File systems

   • JSON structures

   • DOM elements

2. Tree operations

   • Binary trees

   • File explorers

   • Menu structures

3. Divide and conquer

   • Sorting algorithms

   • Search algorithms

   • Mathematical calculations

When Not to Use It

• The problem is simple

• You need maximum performance

• Stack space is limited

• The depth is unknown

Quick Tips

1. ALWAYS have a base case (you’ll be stuck in an infinite loop if you don’t)

2. Move towards the base case

3. Keep it simple

4. Test with small inputs first

Remember

• It's just a function calling itself

• Always have a way to stop

• Always think of recursion as "breaking it down"

• Visualize the steps

• Practice makes perfect

Thank you to everyone who submitted 😃 

GabrielDornelas, E-Sieben, levi-manoel, TheTigerPython, RelyingEarth87, SDKwapis, porrrq, and nhillemann.

Remove the Computer Virus

Your computer might have been infected by a virus! Create a function that finds the viruses in files and removes them from your computer.

Examples

remove_virus("PC Files: spotifysetup.exe, virus.exe, dog.jpg")
output = "PC Files: spotifysetup.exe, dog.jpg"

remove_virus("PC Files: antivirus.exe, cat.pdf, lethalmalware.exe, dangerousvirus.exe ")
output = "PC Files: antivirus.exe, cat.pdf"

remove_virus("PC Files: notvirus.exe, funnycat.gif")
output = "PC Files: notvirus.exe, funnycat.gif")

Notes

• Bad files will contain "virus" or "malware", but "antivirus" and "notvirus" will not be viruses.

• Return "PC Files: Empty" if there are no files left on the computer.

How To Submit Answers

Reply with

• A link to your solution (github, twitter, personal blog, portfolio, replit, etc)

• or if you’re on the web version leave a comment!

• If you want to be mentioned here, I’d prefer if you sent a GitHub link or Replit!

Working on the next video and uh yeah that’s about it.

That’s all from me!

Have a great week, be safe, make good choices, and have fun coding.

If I made a mistake or you have any questions, feel free to comment below or reply to the email!

See you all next week.