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

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

Day 13 of 30. We're going to solve the famous Fibonacci sequence in Ruby. The next videos are going to be all about getting the algorithm better

· Web Dev Zone ·
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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:

Plain Text
 




x


1
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:

Plain Text
 




xxxxxxxxxx
1


 
1
0 1 1 2 3 5 8 13



Second Real Example:

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

Plain Text
 




xxxxxxxxxx
1


 
1
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
Ruby
 




xxxxxxxxxx
1


 
1
def fibonacci(count)
2
  n1 = 0
3
  n2 = 1
4
  sequence = [n1, n2]
5
end
6
 
          
7
puts fibonacci(8)



Step 2

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




xxxxxxxxxx
1
12


 
1
def fibonacci(count)
2
  n1 = 0
3
  n2 = 1
4
  sequence = [n1, n2]
5
  while count > 2 # just a while loop expression that decrements the argument count
6
    count = count - 1
7
  end
8
  return sequence
9
end
10
 
          
11
puts fibonacci(8)
12
# 0 1 1 2 3 5 8 13



Step 3

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




xxxxxxxxxx
1
19


 
1
def fibonacci(count)
2
  n1 = 0
3
  n2 = 1
4
  sequence = [n1, n2]
5
  while count > 2
6
        # sum of the previous 2 numbers
7
    n3 = n1 + n2
8
    sequence.push(n3)
9
10
      # assigning the new numbers to calculate the next number in the sequence
11
    n1 = n2
12
    n2 = n3
13
    count = count - 1
14
  end
15
  return sequence
16
end
17
18
puts fibonacci(8)
19
# 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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Topics:
algorithm, algorithm analysis, coding, coding basics, fibonacci numbers, programming, ruby, tutorial for beginners

Published at DZone with permission of Alexandre Gama . See the original article here.

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