# APL – solving Fizz Buzz

You can become a serverless blackbelt. Enrol in my course Learn you some Lambda best practice for great good! and learn best practices for performance, cost, security, resilience, observability and scalability. By the end of this course, you should be able to make informed decisions on which AWS service to use with Lambda and how to build highly scalable, resilient and cost-efficient serverless applications.

Note: see the rest of the series so far.

This is a classic interview question, and after some experimentation I ended up with the following solution in APL:

$F \ \iota 100$

=> 1 2 Fizz 4 Buzz Fizz 7 8 Fizz Buzz 11 Fizz 13 14 FizzBuzz 16 17 Fizz 19 Buzz Fizz 22 23 Fizz Buzz 26 Fizz 28 29 FizzBuzz 31 32 Fizz 34 Buzz Fizz 37 38 Fizz Buzz 41 Fizz 43 44 FizzBuzz 46 47 Fizz 49 Buzz Fizz 52 53 Fizz Buzz 56 Fizz 58 59 FizzBuzz 61 62 Fizz 64 Buzz Fizz 67 68 Fizz Buzz 71 Fizz 73 74 FizzBuzz 76 77 Fizz 79 Buzz Fizz 82 83 Fizz Buzz 86 Fizz 88 89 FizzBuzz 91 92 Fizz 94 Buzz Fizz 97 98 Fizz Buzz

The answer looks correct, though this is perhaps not the most straight forward solution, so let’s walk through what’s happening here:

• first turn the input array $\omega$ into booleans to determine if they’re divisible by 3 $0=3 | \omega$ or 5 $0=5 | \omega$

$0 = 3 | \omega$ : 0 0 1 0 0 1 0 0 1 0 0 1 …

$0 = 5 | \omega$ : 0 0 0 0 1 0 0 0 0 1 0 0 …

• assuming that $\omega$ has length of 100, then transform the boolean arrays from the previous step so that 1s becomes 101s (for those divisible by 3) and 102s (for those divisible by 5)

$(1 + \rho \omega) \times 0 = 3 | \omega$ : 0 0 101 0 0 101 0 0 101 0 0 101…

$(2 + \rho \omega) \times 0 = 5 | \omega$ : 0 0 0 0 102 0 0 0 0 102 0 0 0…

• add the two arrays together, so that those divisible by 3 has value 101, divisible by 5 has value 102 and those divisible by 15 has value 203

0 0 101 0 102 101 0 0 101 102 0 101 0 0 203 0 0 101 …

• apply minimum $\lfloor$ to this array with 103 being the operand, so now numbers divisible by 15 has value 103 instead of 203

0 0 101 0 102 101 0 0 101 102 0 101 0 0 103 0 0 101 …

• apply maximum $\lceil$ to this array with the input array $\omega$ to end up with the following

1 2 101 4 102 101 7 8 101 102 11 101 13 14 103 16 17 101

• use this array as index for an array that is made up of the input array $\omega$ with ‘Fizz’ ‘Buzz’ ‘FizzBuzz’ added to the end at index position 101, 102 and 103 respectively

Subscribe to my newsletter

Hi, I’m Yan. I’m an AWS Serverless Hero and the author of Production-Ready Serverless.

I specialise in rapidly transitioning teams to serverless and building production-ready services on AWS.

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.

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!

Are you working with Serverless and looking for expert training to level-up your skills? Or are you looking for a solid foundation to start from? Look no further, register for my Production-Ready Serverless workshop to learn how to build production-grade Serverless applications!