Ruby
## Day 15 of 30 - Ruby Coding Challenge - Fibonacci Sequence Recursively

## Fibonacci Recursively in Theory

## Fibonacci Recursively in Ruby

Hey friends!

This is the blog post version of the Youtube video from the 30 Ruby Coding Challenges in 30 Days series

Today we’ll solve the previous Fibonacci problem using the dreaded recursion approach

A little bit of theory was explored in this video and today I’ll straight to the point

Just to remember:

- A recursive method is a method that calls itself
- A recursive method usually solves a smallest version of the bigger (original) problem

When it comes to Fibonacci, the definition already gives us a hint of how to solve it recursively:

To get the next number in a sequence, you have to sum the previous two numbers

Let’s say that we want the first 8 numbers in the Fibonacci sequence:

```
0 1 1 2 3 5 8 13
```

Notice that to get the value 13:

- we need to first calculate the first 7 numbers of a Fibonacci sequence

But to get the value 8:

- we need to first calculate the first 6 numbers of a Fibonacci sequence

But to get the value 5:

- we need to first calculate the first 5 numbers of a Fibonacci sequence

Yup, you got it : ) We need to calculate the Fibonacci number of the previous 2 numbers

**Version 1**

Notice that the **count** argument controls when to stop the method calling itself

```
def fibonacci(count)
if count <= 1
count
else
fibonacci(count - 1) + fibonacci(count - 2)
end
end
```

**Version 2**

In 1 line, we could use a ternary operation:

```
def fibonacci(count)
count <= 1 ? count : fibonacci(count - 1) + fibonacci(count - 2)
end
puts fibonacci(8)
# 0 1 1 2 3 5 8 13 21
```

Great!

Probably you may already know that this approach doesn’t have a good performance but this is something for another post :)

Thanks for the visit and see you in the next coding challenge!

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