Day 13 of 30 Ruby Coding Challenge - Fibonacci Sequence in Ruby

Hey friends!

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

Fancy Fibonacci Algorithm Definition

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

One important point: The Fibonacci sequence already starts with 0 and 1 as the first 2 numbers

Here is a sequence to help you out a bit more:

0 1 1 2 3 5 8 13 21 34 55 88 ...

Perfect. Now we want to solve the following puzzle:

We want to calculate the first N numbers in a Fibonacci sequence

First Real Example:

I want to calculate the first 8 numbers in a Fibonacci sequence:

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0 1 1 2 3 5 8 13

Second Real Example:

I want to calculate the first 10 numbers in a Fibonacci sequence:

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0 1 1 2 3 5 8 13 21 34

I’m pretty sure you got it : )

Fibonacci Algorithm in Ruby

Step 1

• let’s create the fibonacci() method
• then we’ll start the sequence with 0 and 1

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def fibonacci(count)

  n1 = 0

  n2 = 1

  sequence = [n1, n2]

end

puts fibonacci(8)

Step 2

• because the list starts with 2 numbers, we can calculate the next one using a while loop

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def fibonacci(count)

  n1 = 0

  n2 = 1

  sequence = [n1, n2]

  while count > 2 # just a while loop expression that decrements the argument count

    count = count - 1

  end

  return sequence

end

puts fibonacci(8)

# 0 1 1 2 3 5 8 13

Step 3

• the next number is the sum of the previous 2 numbers

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def fibonacci(count)

  n1 = 0

  n2 = 1

  sequence = [n1, n2]

  while count > 2

        # sum of the previous 2 numbers

    n3 = n1 + n2

    sequence.push(n3)

      # assigning the new numbers to calculate the next number in the sequence

    n1 = n2

    n2 = n3

    count = count - 1

  end

  return sequence

end

puts fibonacci(8)

# 0 1 1 2 3 5 8 13

Pretty simple, isn’t it?

Although the code is simple, it’s far from a good code design because:

• it lacks readability
• it updates an argument received in the method
• it has too many local variables

To be honest, sometimes (and even most of the time), a good code design is a matter of context and personal taste, and maybe you might think that this code is already good enough, and I don’t blame you. However, I’ll solve the same problem using a different approach that probably you might like better

Hope to see you in the next Ruby Coding Challenge : )

Don’t forget to come by and say hi Alex
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