Advent of Code F# – Day 18

The source code for this post (both Part 1 and Part 2) is available here and you can click here to see my solutions for the other Advent of Code challenges.

Description for today’s challenge is here.

 

This is a modified version of the Day 6 challenge, with a twist of course.

So, we’ll start by creating a 100×100 2D array to represent our grid of lights. As per the instruction, we’ll read the input and use # to set the original state of a light to ON, and . to set the original state of a light to OFF.

day18_01

Next, let’s add a function to count the number of neighbours that are ON, whilst taking into account that lights on the edge of the grid won’t have all 8 neighbours:

day18_02

Then we’ll simulate 100 steps, each step would use the state from the previous step in a fold:

day18_03

Finally, count the number of lights that are ON in the state after 100 steps:

day18_04v2

 

Part 2

All else stays the same, we just need to inject additional logic to check if the light is one of the corner lights in a few places.

First, let’s add a function to determine if a light is in the corner:

day18_05

and now we need to use it when setting the initial state for our grid:

day18_06

as well as when we step from one state to the next:

day18_07

and that’s it. After you made these couple of changes, all the rest of the code from Part 1 would work like before.

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 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.

Hire me.


Check out my new 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. Including basic concepts, HTTP and event triggers, activities, callbacks, nested workflows, design patterns and best practices.

Get Your Copy