Day 17 Ruby Coding Challenge  Sum Even Numbers in Fibonacci Sequence
Day 17 of 30. We're going to sum all the even numbers in a given Fibonacci sequence using a better code design in Ruby
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This is the blog post version of the Youtube video from the 30 Ruby Coding Challenges in 30 Days series
Today, we want to solve the previous problem in a more Ruby Way
I want to sum all even numbers in a Fibonacci sequence
Last Algorithm Version
This was the last algorithm version of the problem:
def fibonacci_sum(count)
sum = 0
number = 0
sequence = []
(0..count).each do item
number = item if item <= 1
number = sequence[1] + sequence[2] if item > 1
sequence << number
sum += number if number % 2 == 0
end
sum
end
The code is not that great for a couple of reasons:
 Too many local variables to manipulate.
 Two main responsibilities: create the Fibonacci sequence AND validate even numbers.
The two main reasons above leave us with code that's difficult to read, and therefore, difficult to maintain. Fewer friends in our team, right?
I’m going to try to get rid of these problems. Let’s get into it!
Better Algorithm Version  Ruby Way
I’m going to break the refactoring into a few small steps
Step 1  Splitting Responsibilities
Let’s create a new method do generate only the Fibonacci sequence
xxxxxxxxxx
def fibonacci(count)
sequence = []
(0..count).each do number
sequence << number if number <= 1
sequence << sequence[1] + sequence[2] if number > 1
end
sequence
end
Then we’re going to create the method to sum even numbers based on the generated sequence
xxxxxxxxxx
def fibonacci(count)
sequence = []
(0..count).each do number
sequence << number if number <= 1
sequence << sequence[1] + sequence[2] if number > 1
end
sequence
end
def sum(array)
# magic here
end
puts sum(fibonacci(10))
Step 2  Sum of Even Numbers
Now, we just need to sum all the even numbers, given an array of numbers.
As we did previously here, I’m going to use a Ruby symbol, which allows us to reduce a list of items into a single number by applying an operation:
xxxxxxxxxx
def sum(array)
array.select { number number % 2 == 0 }.reduce(:+)
end
The complete code would be:
xxxxxxxxxx
def fibonacci(count)
sequence = []
(0..count).each do number
sequence << number if number <= 1
sequence << sequence[1] + sequence[2] if number > 1
end
sequence
end
def sum(array)
array.select { number number % 2 == 0 }.reduce(:+)
end
puts sum(fibonacci(10))
That’s it! A little bit better version of the previous problem and I hope you liked it!
Do you have a better/different version? Drop that in the comments and bring more healthy discussions!
Thanks for the visit and see you in the next coding challenge. Don’t forget to come by and say hi!
Published at DZone with permission of Alexandre Gama. See the original article here.
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