Project Euler – Problem 2 Solution

You can become a serverless blackbelt. Enrol to my 4-week online workshop Production-Ready Serverless and gain hands-on experience building something from scratch using serverless technologies. At the end of the workshop, you should have a broader view of the challenges you will face as your serverless architecture matures and expands. You should also have a firm grasp on when serverless is a good fit for your system as well as common pitfalls you need to avoid. Sign up now and get 15% discount with the code yanprs15!

Problem

Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

Find the sum of all the even-valued terms in the sequence which do not exceed four million.

Solution

Here’s my solution in F#:

let fibonacciSeq = Seq.unfold (fun (current, next) -> Some(current, (next, current + next))) (0, 1)

let fibTotal =
    fibonacciSeq
    |> Seq.takeWhile (fun n -> n < 4000000)
    |> Seq.filter (fun n -> n % 2 = 0)
    |> Seq.sum

Here I’ve used a sequence, whilst a sequence is similar to a list or array in F# in that it holds a series of elements, there’s a crucial difference, each sequence element is computed only as required so it provides better performance than a list in situations which not all elements are used. If that sounds familiar to you, that’s because a sequence is basically an IEnumerable<T>!

In the first step of this code I’m building up the fibonacci sequence using the Seq.unfold function which given an initial value, generates a sequence by continuously applying some computation to work out each subsequent element in the sequence:

let fibonacciSeq = Seq.unfold (fun (current, next) -> Some(current, (next, current + next))) (0, 1)

This sequence, if iterated through, will contain all the numbers in the fibonacci sequence to infinity, which is why in the next line I’ve specified that we should take values from the sequence until the value exceeds 4 million:

fibonacciSeq
|> Seq.takeWhile (fun n -> n < 4000000)
&#91;/code&#93;

The next two lines then identifies and sums all the even numbers in the sequence:

&#91;code lang="fsharp"&#93;
|> Seq.filter (fun n -> n % 2 = 0) // only interested in even numbers
|> Seq.sum // add them up!
Liked this article? Support me on Patreon and get direct help from me via a private Slack channel or 1-2-1 mentoring.
Subscribe to my newsletter


Hi, I’m Yan. I’m an AWS Serverless Hero and I help companies go faster for less by adopting serverless technologies successfully.

Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.

Hire me.


Skill up your serverless game with this hands-on workshop.

My 4-week Production-Ready Serverless online workshop is back!

This course takes you through building a production-ready serverless web application from testing, deployment, security, all the way through to observability. The motivation for this course is to give you hands-on experience building something with serverless technologies while giving you a broader view of the challenges you will face as the architecture matures and expands.

We will start at the basics and give you a firm introduction to Lambda and all the relevant concepts and service features (including the latest announcements in 2020). And then gradually ramping up and cover a wide array of topics such as API security, testing strategies, CI/CD, secret management, and operational best practices for monitoring and troubleshooting.

If you enrol now you can also get 15% OFF with the promo code “yanprs15”.

Enrol now and SAVE 15%.


Check out my new podcast Real-World Serverless where I talk with engineers who are building amazing things with serverless technologies and discuss the real-world use cases and challenges they face. If you’re interested in what people are actually doing with serverless and what it’s really like to be working with serverless day-to-day, then this is the podcast for you.


Check out my new course, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. We will also cover latest features from re:Invent 2019 such as Provisioned Concurrency and Lambda Destinations. Enrol now and start learning!


Check out my video course, Complete Guide to AWS Step Functions. In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. There is something for everyone from beginners to more advanced users looking for design patterns and best practices. Enrol now and start learning!