---
title: Rightward Assignment in Ruby - Day 04 - Advent of Code 2023
slug: rightward-assignment-in-ruby-day-04-advent-of-code-2023
published_at: 2023-12-04 18:00:27 +0000
updated_at: 2026-03-04 20:15:18 +0000
summary: 
description: Dive into the Advent of Code 2023 Day 4 puzzle with a Ruby twist! In this episode, titled \&quot;Scratch Cards,\&quot; we’ll focus on harnessing the power of Ruby&#39;s rightward assignment feature for a challenge.  We start by setting up our input data, consisting of winning numbers and our own numbers, separated by a pipe operator. The goal is to determine how often our numbers appear in the winning numbers, with points doubling for each match. This episode walks you through each process step, from parsing the input with here-docs to utilizing rightward assignment for efficient code structuring.  Our journey includes pattern matching and array manipulation. The second part of the puzzle adds a twist, where scratch cards yield more cards instead of points, leading to a cascading effect in card duplication.  Advent of Code: https://adventofcode.com/ My Solutions: https://gist.github.com/cjavdev/d15a2a4ffed6c840c2fb28a093e9f927/ Playlist https://www.youtube.com/playlist?list=PLS6F722u-R6KYlGyUv65EFpGKl2Esmurr  #adventofcode  #ruby
tags: [cjav_dev, web development tutorials, web development for beginners, vim, ruby, advent of code, advent of code 2023, rightward assignment, rightward assignment in ruby, advent of code day 4, advent of code scratch cards, advent of code scratchers, aoc 2023, ruby advent of code]
views: 440
author: CJ Avilla
url: https://www.cjav.dev/videos/rightward-assignment-in-ruby-day-04-advent-of-code-2023
youtube_url: https://www.youtube.com/watch?v=W1Z0VCdRwag
youtube_id: W1Z0VCdRwag
embed_url: https://www.youtube.com/embed/W1Z0VCdRwag
thumbnail_url: https://i.ytimg.com/vi/W1Z0VCdRwag/hqdefault.jpg
type: video
---

# Rightward Assignment in Ruby - Day 04 - Advent of Code 2023

*Published: December 04, 2023*
*Views: 440*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=W1Z0VCdRwag)

[![Rightward Assignment in Ruby - Day 04 - Advent of Code 2023](https://i.ytimg.com/vi/W1Z0VCdRwag/hqdefault.jpg)](https://www.youtube.com/watch?v=W1Z0VCdRwag)

## Description

Dive into the Advent of Code 2023 Day 4 puzzle with a Ruby twist! In this episode, titled &quot;Scratch Cards,&quot; we’ll focus on harnessing the power of Ruby&#39;s rightward assignment feature for a challenge.

We start by setting up our input data, consisting of winning numbers and our own numbers, separated by a pipe operator. The goal is to determine how often our numbers appear in the winning numbers, with points doubling for each match. This episode walks you through each process step, from parsing the input with here-docs to utilizing rightward assignment for efficient code structuring.

Our journey includes pattern matching and array manipulation. The second part of the puzzle adds a twist, where scratch cards yield more cards instead of points, leading to a cascading effect in card duplication.

Advent of Code: https://adventofcode.com/
My Solutions: https://gist.github.com/cjavdev/d15a2a4ffed6c840c2fb28a093e9f927/
Playlist https://www.youtube.com/playlist?list=PLS6F722u-R6KYlGyUv65EFpGKl2Esmurr

#adventofcode  #ruby

## Transcript

what&#39;s up welcome back in this episode you&#39;re going to see how to solve day four of the Advent of code for 2023 this one&#39;s called scratch cards and we&#39;re going to learn all about right word assignment so today&#39;s exercise we&#39;re going to strengthen and focus on building our right word assignment muscle right word assignment is a new feature of Ruby a newish feature of Ruby and we&#39;re going to try and use that as much as possible just for fun to practice and strengthen and learn more about right word assignment in this episode we we made it up through the gondola to another island in the sky this one is called island island and when we get there we have to do something with an elf related to scratch cards scratch cards are these little things that you get at 7-Eleven or the corner store and you take a coin and you scratch off and you hope that you won some thing it&#39;s like a gambling type situation this is our input in this this exercise we have some set of winning numbers those are on the left side of this pipe operator and then we have our numbers which are on the right side of the the pipe operator and we want to see how many times our numbers appear in the winning numbers and the for the first number that appears in the winning numbers we get one point and the second number that appears in that in the winning numbers our points double so every time we have a winning number our points are going to double so it&#39;s going to be like starting at Z 1 2 4 8 16 32 and so on in this example above the numbers 41 48 83 86 and 17 these are the winning numbers and we have these numbers and on the right hand side four of them match the winning numbers right so we see 83 is a winning number and 17 is a winning number and 48 is a winning number and 86 is also a winning number so 83 86 17 and 48 are winning in this row that means that we get one two four eight points right because every time we have a winning number match we are doubling the score what we want to do is go through figure out how many points there are in total for the input so let&#39;s grab the input we&#39;ll pop open in the terminal here and get started so we&#39;ll say input is is equal to oo that&#39;s a good question I don&#39;t know if we can do right word assignment with here dos that would be a fun one to try out let&#39;s just see p input okay so if we were to change this around can we do something like this does that work no oh wait here we need to print this out what that totally works okay that&#39;s a freaky looking freaky looking thing all right let&#39;s see all right so now we&#39;re going to have input. each line this is going to be our data okay so what am I doing here with this rocket ship operator this is right word assignment instead of saying input is equal to this here doc value we&#39;re switching it up and we&#39;re pointing it the other way we&#39;re rightward assigning the value of input into this now in in the case of a her do that&#39;s super funky because this is happening after the start of the her do which makes it look even weirder but we&#39;re just having fun right now okay so now what we want to do is we want to map over each of these cards and we want to split out the card so that we have the winning numbers and our numbers right there&#39;s a couple different ways we can split this up I think it might make sense to use yeah again we can use right word assignment here so we can say card.it and if we just split it on Space what does that give us yeah so if we split it on Space we can break out card and then this number and then a bunch of numbers and then the pipe operator yeah so let&#39;s do this so we&#39;re going to use right word assignment and we&#39;re going to destructure the label and then the ID of the card and then we&#39;ll use Splat to grab all of the numbers okay and this Splat operator is going to hold all of this including the pipe so if we just print out numbers right now we&#39;re going to see arrays where we have the string values for the numbers and then we have this pipe operator what we can do now is we can again uh use right word assignment and what&#39;s cool is that because we want to collect everything on the left into an array and then we want to collect everything on the right to an array and we want to like just identify or like split on this pipe what we can do is say star winning and then the pipe operator and then ours or something right so so then if we just print ours you&#39;ll see 83 86 6 31 17 etc etc so this is our numbers so by using this pipe operator with right word assignment we&#39;re pattern matching we&#39;re saying that grab everything up to the point where we match the pipe and then grab everything after we match the pipe so that is pretty cool so if we and also maybe we print the array of winning and hours like this so we can see so now we have these two arrays which is perfect and what we can do is we can use the we can use the Amper sand operator to get the union of those two arrays so that&#39;s it&#39;s like the set Union between the two arrays so now we can see 48 83 86 17 that is the values that are in the right side that match the values that are in the left side and what this tells tells us is how many matches there are so if we grab off the size and we store that into oh we got to use right word assignment again all right let&#39;s say this is like the yeah the matches or like the match count or something right in order to find the points that we get for the match count what we want to do is if you look at the pattern like 1 2 4 8 16 those are really familiar numbers because those are the values you get in binary if you toggle on the furthest bit so there&#39;s probably something super fancy we could do with binary here but what I wanted to do is just say if like if the match count is greater than zero then we&#39;re going to return match count uh r two raised to the match count minus one right otherwise we&#39;re going to return zero and this is going to give us some result I guess we could use the right word op the right word assignment again here so uh scores and then we&#39;ll P scores let just to see what we get back all right so 8 22 one and then if we uh get the sum of those now we get 13 which was the example input okay awesome so now let&#39;s grab our let&#39;s grab our puzzle input and we&#39;ll drop this as always here at the end and now we&#39;re going to switch from using so now we need to do data. readlines is data and we&#39;ll run this again and 15205 is that our number for part one 1525 boom that is the puzzle answer for part one a lot of rightward assignments so you probably aren&#39;t going to see much Ruby looking like this if you&#39;re looking around because not many folks are using right word assignment yet but this is a good opportunity using using this Advent of code is an awesome opportunity to learn about different features of the languages that you&#39;re using and if you line them up like this gosh it almost looks hasc or something hasc or rascally I don&#39;t know hard to say but right word assignment hey it&#39;s it&#39;s pretty interesting okay oh and here we have a warning that says we have label is assigned but it&#39;s unused so what we can do is if we&#39;re not actually using label we can put underscore same thing with ID so we can actually just make those underscores and that says just ignore ignore the one that&#39;s in this place and we still get one 5 205 as our answer this is looking pretty sweet let&#39;s move on to part two just as you&#39;re about to report your findings to the elf one of you realizes that the rules have actually been printed on the back of every card this whole time so there&#39;s no such thing as points instead scratch cards only cause you to win more scratch cards if you&#39;ve been to if you&#39;ve been to 7-Eleven or one of these corner stores and you&#39;ve bought a scratch card you know that a lot of times when you scratch off the card the winning thing is other cards that is the thing that you win and so in this case this is this is a play on that so we&#39;re going to win copies of the scratch cards that are below the winning card equal to the number of matches so if card 10 is going to have five matches then you&#39;re going to win copies of 11 12 13 and 15 so in this example card one has four matching numbers right we already saw that and that means that we need to make a copy of cards to 2 3 4 and five the original card two has two rch two matching numbers so when we go to like actually process two we&#39;re going to win one copy of three and four from the original card two and we&#39;re also going to win uh a copy of three and four from the copy of card two so this kind of complicates our our Loop a little bit and so rather than just winning four matches here we need to win four matches and and then duplicate the four cards below us and keep track and so that&#39;s what we&#39;re going to do so once all of the originals and the copies have been processed you end up with one instance of card one two of card two four of card three and so on so we&#39;re going to process all the original scratch cards until no more are one and then our answer for part two is how many total scratch cards we end up with so it&#39;s going to be like this cascading thing right where we start at the top and then it falls down and we&#39;re make more and more as we go all right so we have our match count and we also need to somehow keep track of how many cards we have because we also now need to know the ID of our current cards so that we can apply it to the next card below us I think we actually do want to use this ID number so we&#39;re going to comment out our real data and let&#39;s grab the ID and the ID itself isn&#39;t going to work just as it is because if we look at it if we print the ID here the ID has a colon in it and so what we want is the numeric ID so that we can work with that card number and like future card numbers because we&#39;re going to want to like increment forward so let&#39;s say that again using right word assignment id. 2i is now ID so now if we print out ID down here we should get back these numbers 1 2 3 4 5 six great okay I&#39;m going to comment out scores for now but so now that we have the IDS we need to figure out how to make duplicates as we&#39;re working through this and in order to keep track of those I think we want some counter and the way we&#39;re going to do this is with a has. new of HK and this default dictionary the way that we&#39;re initializing this we&#39;re passing it a block the block passed to new will be executed every time we encounter a new key into this counter hash and rather than setting it to zero we want to set it to one because we have at least one copy of all the cards so this counter is really going to give us like the number of each card card count card counts right and this is going to be like an index of the ID points at the count of that card or whatever like the number of times we have that it&#39;s like number of copies of that card okay and then at the end what we&#39;re going to do is we&#39;ll return the values of these counts I think what we want to do is as we&#39;re iterating through and we have our match count we need to do something like match count. times do I and then that&#39;s going to let us know how many cards down we need to go so we&#39;re going to go like card counts at id+ I uh plus one right so ID or I is going to start at zero so if we&#39;re on card one this is going to iterate to card two then card three then card four then card five and every time we encounter one of these we want to increment the count at that location by one right and that should give us if we were just doing one copy at a time that would give us that that one copy for the original but because we also need to apply it to Future cards based on the copies of the current card we need to uh go through um card counts of id. times so for the first card we&#39;ll go one time and then for the second card it should have two in here so then this is going to go twice and we actually don&#39;t need a counter for that okay I think I don&#39;t know let&#39;s just see what we get for for card counts at the end here P card counts all right so we have one of one two two four card threes eight card fours 14 card fives and one card six and I think that&#39;s actually what we expect here 1 2 4 8 14 1 1 2 48 141 okay so now what we want to do is just I think we just need to add up values. sum and we get 30 and 30 matches the number of scratch cards in the demo so then if we just reenable the actual stuff here 618 9740 618 9740 boom that is the answer for part two awesome awesome okay how could we clean this up if you&#39;ve got a Keen Eye you are noticing that this is a left word assignment this is the same as saying card counts plus equals 1 the other way I don&#39;t actually know if we can do card counts at ID + 1+ i+ one into card counts like this will this work I don&#39;t think this works yeah because the right hand side this is not a variable this is like indexing into a hash I&#39;m not sure that&#39;s even possible I&#39;m yeah I don&#39;t know maybe we would need to do some other thing for this one I don&#39;t know if someone else knows that answer let me know I think we&#39;ll probably have to just call card counts. set or some other method yeah instead of right word assignment obviously we&#39;re like calling methods all over the place here like size 2y map Etc Etc but yeah I don&#39;t know I think it&#39;s neat so yeah that was fun cool perhaps in a future episode we will talk about how we might have done this with some bit fiddling because I think you could do something like a match count like some sort of like shifting right like we want to do one or yeah zero one shift m count some number of times to get us back that number but for now I think this is pretty sweet and I&#39;m happy with it thank you so much for watching if you are enjoying this series please don&#39;t forget to subscribe and we&#39;ll see you in the next one cheers

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