---
title: Match and Scan - Day 01 - Advent of Code 2023
slug: match-and-scan-day-01-advent-of-code-2023
published_at: 2023-12-01 22:05:00 +0000
updated_at: 2026-03-04 20:15:19 +0000
summary: 
description: Let&#39;s solve Day 1 of Advent of Code 2023 in Ruby! We&#39;ll parse a trebuchet calibration log file, extracting the first and last digits from each line, whether they&#39;re numerals or spelled-out words. By summing these two-digit numbers, we get the calibration value.  It&#39;s a fun logic puzzle with regular expressions, arrays and hashes in a Ruby script. The code is concise but effective for this coding challenge.  Overall it&#39;s a great beginner-friendly Advent of Code solution, showing some clever Ruby tricks for this text parsing and calculation problem.  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, advent of code ruby]
views: 1051
author: CJ Avilla
url: https://www.cjav.dev/videos/match-and-scan-day-01-advent-of-code-2023
youtube_url: https://www.youtube.com/watch?v=lrJfC2dF84k
youtube_id: lrJfC2dF84k
embed_url: https://www.youtube.com/embed/lrJfC2dF84k
thumbnail_url: https://i.ytimg.com/vi/lrJfC2dF84k/hqdefault.jpg
type: video
---

# Match and Scan - Day 01 - Advent of Code 2023

*Published: December 01, 2023*
*Views: 1051*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=lrJfC2dF84k)

[![Match and Scan - Day 01 - Advent of Code 2023](https://i.ytimg.com/vi/lrJfC2dF84k/hqdefault.jpg)](https://www.youtube.com/watch?v=lrJfC2dF84k)

## Description

Let&#39;s solve Day 1 of Advent of Code 2023 in Ruby! We&#39;ll parse a trebuchet calibration log file, extracting the first and last digits from each line, whether they&#39;re numerals or spelled-out words. By summing these two-digit numbers, we get the calibration value.

It&#39;s a fun logic puzzle with regular expressions, arrays and hashes in a Ruby script. The code is concise but effective for this coding challenge.

Overall it&#39;s a great beginner-friendly Advent of Code solution, showing some clever Ruby tricks for this text parsing and calculation problem.

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 we&#39;re kicking off the Advent of code for 2023 this is day one and we&#39;re talking about a trebuchet this is uh you know Contraption from medieval times where you&#39;re going to throw a flaming cannonball at a castle or something right and so we&#39;ve got one of these trebuchets and they have a calibration document and the calibration document has been amended it&#39;s been edited there&#39;s some a PR that was made by a young elf who was just super excited to show off her art skills and so we&#39;ve got to go through and figure out some things about this calibration document so each line of the calibration document originally contained some calibration value so each of these lines is going to have some calibration value and we need to figure out what that calibration value was and so we can go through this example input here and the uh the calibration numbers are the first digit that we encounter uh added with the last digit that we encounter before the end of the line and that&#39;s going to form a two-digit number so we&#39;re kind of just like look from the front of the string for a number and then we&#39;re going to look from the back of the string for a number and that&#39;s going to give us two digits we&#39;re going to squish those together and that gives us the calibration value for a given line then we&#39;re going to take all of the calibration values for all of the lines add them up and we should get some number so in this example here we should get back 142 let&#39;s put pipe open day one Ruby here and just say that our like our input is going to be this this thing so we&#39;ll use a little here dock here and we&#39;ll say that our input is this now we&#39;re going to say like input dot each line do line so again like each line is going to have some calibration number so maybe we&#39;ll say uh calibration number is line and for now what we can do is scan for digits so what we want to do is find digits that are in that line and we need to figure out we don&#39;t want to just sum up all the digits in the line we kind of need to like pull off the first one and pull off the last one so if we scan for digits in the line what does that give us so let&#39;s just P calibration number for now and see what that giv gives us so in the bottom I&#39;m using the exclamation point and Ruby to run this Ruby uh this Ruby file directly here from Vim so in day one from this input our first line gives us one and two the second line gives us three and eight the third line gives us 1 2 3 4 5 1 2 3 4 5 and the last line gives us seven now in the case of seven it&#39;s a little odd if we have a single number that we found from looking from the front and the the same number when we looked from the back then we want to combine that number with itself so or like we&#39;re going to put two sevens next to each other to give us the number 77 um so what we really want out of this is 1 and two 3 and 8 one and five and then seven and seven so let&#39;s see if we can get this to behave as we expect we actually don&#39;t want to map to I right now we just want to like grab the digits off and then we&#39;re going to combine them later so what we can do is we can scan the line and get back this calibr uh number uh actually so by scanning the line we&#39;re going to get some uh some array and let&#39;s just map that uh or how do we want to do this okay so this is going to be like um uh digits okay and then we&#39;ll say digits. first plus digits. last assuming that this is an array of strings and let&#39;s just see what this gives us okay we don&#39;t actually want it to add the numbers we want it to give us these numbers back so 12 38 1577 so 12 38 1577 that looks good so now what we want to do is we actually want to like take the string concatenated version of that and convert that into an integer so that should give us number values for each of those that&#39;s great now what we want to do is we want to sum those up so I think what can actually do maybe is just say do sum is that true uh nope okay uh so um oh maybe we have to put it at the end do sum is that going to work uh no oh because we&#39;re not actually printing anything with the result so we&#39;ll take our result here and we&#39;ll P result uh that&#39;s way too big 3457 so we expecting uh 142 so some this seems like it&#39;s not actually working as expected H oh because each line isn&#39;t actually mapping so we&#39;ll do do map okay now we get 142 so by adding map here each line is going to like return an iterator and we can just throw map onto the end of the iterator so that the result of calling this block gives us back an array and that array will contain the return values from the Block and then we can call do sum that gives us a result back which is 142 so that is the example the answer for the the input example now we want to sum up all the values in our test input so down here I can get my puzzle input I&#39;ll just grab all of this and to keep things easy I&#39;m going to put this inside of the same file in the end and what we can do is instead of saying uh input. each line we can say data readlines and rerun this and we get the value 55002 which was my puzzle answer for part one that&#39;s it that&#39;s part one we&#39;ve solved part one now part two your calculation isn&#39;t quite right it looks like some of the digits are actually spelled out with letters oh my gosh okay so sometimes the digit is like a digit that we would expect 1 2 3 4 5 and sometimes it&#39;s spelled out o n t wo t h re e e so they give us exactly the ones that we can expect here and what we want to do is look at some of these calibration lines now and now we have to figure out a little different approach here so let&#39;s just comment this out this is part one okay so now for uh for part two what we want to do is maybe something very similar here right um but we can&#39;t just scan for D okay because instead of scanning for D we need to scan for also potentially um the words that represent those digits uh so let&#39;s just see if we can get this uh if we can get this working so for our input now so this is like input part one um and then we&#39;re gonna have input part two actually let&#39;s put it down here okay all right we&#39;ll just comment out part one entirely okay so for part two we&#39;ve got some new input so our new input looks like this okay all right and here we can just say uh input. each line and we want to do something with those lines and so for now let&#39;s just P digits and see what we get okay so in some cases like in the second line here eight W3 we aren&#39;t getting any result because none of those are actually digits so one thing that we can do is add in here like we want either digit or the word one or to or three or four or five or six or seven or eight or nine I think that should do it okay so now we&#39;ve got sort of uh some results that look good um and technically we could now convert these into some number values so if we look at all of the possible values that we&#39;re getting back when we do this scan thing we could also do like a match I guess so that if we do like match um yeah the the difference is that scan is going to give us the entire like array of all those results and match will give us uh yeah so I&#39;m I&#39;m stumbling because I think what we want to do is we only want to look left to right and find the first instance and then we&#39;re going to want to look right to left left and find the first instance so by uh by using scan here we&#39;re going to get back an array of all of the values that match what&#39;s in here but some of those don&#39;t actually give us what we want I think um so for instance like here where we have one8 like o n e e g HT like these are overlapping right this e is shared by both one and by eight and so we need some way to figure out okay if we&#39;re counting from the left yes we want the one but if we&#39;re counting from the right we want the eight and so we might not get that exactly as we expect if we look at the final result here we see 1 2 3 4 eight is not in here anywhere so if we&#39;re counting from the right we would be missing eight so instead I think what we want to do instead of scanning for all of the results that match these I think we want to do match and we only want to get like the first one so let&#39;s just see that looks like okay so now we have this match data and I I think if we do like at zero we&#39;ll get back okay so two was the first one then eight then one okay that&#39;s great then what we can do is maybe we build a dictionary that will convert from the word to the number so maybe we do like uh word to digit we&#39;ll do one: one 2: two 3 to 3 four to four there&#39;s like uh some rule in Advent of code for this there this year that you&#39;re not allowed to use AI for the problems and um I don&#39;t know if this counts uh I&#39;m hoping it doesn&#39;t count but also I&#39;m not super serious about the leaderboard and usually I don&#39;t solve the problem until well into the next day so I think it&#39;s all gravy um and then maybe zero I don&#39;t know if that I can&#39;t remember if that matters okay so what we want to do now is like take this match or this like word um to digit and pass in our thing here and now we&#39;re getting back the we&#39;re always getting back digits now so that&#39;s cool um okay so the next thing we want to do I guess this like this is only going to give us the first the first digit so from the left this will give us the first digit so if we&#39;re like printing out the line uh right above the digit that we&#39;re getting so two that&#39;s two eight is eight one is not in here oh here it is one okay one two is two that&#39;s great so four we get four so this gives us both the words and the digits if we encounter a digit so that&#39;s fantastic okay so the next thing we want to do um is find the last word and so the way that I solved This was um was I I went the other way around so this is kind of like the the first and then um last and I just uh to to solve this I like reversed I want to reverse the line so I&#39;m just going to like take the entire line flip it around backwards and then search through and when I&#39;m searching through um each like numeric digit is going to be the same and so um for the words though instead of O and E I&#39;m going to do um E and O right we&#39;re just going to do the words and we&#39;re going to spell them backwards so instead of going through and like manually reversing these what I&#39;m going to do is pull all of this out and we&#39;re going to just replace this using the keys that are in our word to digit uh dictionary here so we&#39;ll just say word to digit dokeys and then here we can do word to digit keys and then we&#39;ll just do it well them in Reverse so word to digigit do keys. map uh reverse okay um what is this uh unused variable results oh gosh there&#39;s so much so much messiness okay and then at the end we should get like uh some first plus last and that&#39;s going to give us a two character string or it should and we&#39;ll just like see what this looks like uh first plus last undefined for nil class okay oh right because if we get a match we also need to reverse the match and still sad okay um oh and in we also okay so for our regular expression here we also need to join on the pipe operator so that it&#39;s like a bunch of ores uh so we&#39;ll do that in both cases um okay let&#39;s see what we get all right look at that okay so now we have a bunch of uh sort of looking number looking thingies we&#39;ll convert those into integers and we get back a bunch of integers do sum and now we cross our fingers and hope that this matches our example input so 281 is matching 281 awesome so can we just swap out input. each line for data. readlines and run it again 55093 55093 boom okay awesome so that was fun uh and sort of I don&#39;t know it&#39;s a little hacky right we&#39;re doing some a bunch of reversing there&#39;s also like uh we could probably cache some of this like re so we don&#39;t have to do all the string reversing um several times we can probably do like you know uh key or like um words is word to digit dokeys and then our words is words. map reverse that way we only do it once and then we could say this is words and this is our our wordss and now we should get the same result and we do uh anything else that we could probably clean up in here I don&#39;t know I mean it&#39;s this is relatively like concise um another way that you could do this is sort of like do a an an iterator from like zero do up to the length of some line um and then inside of that maybe you do like uh three times do and then you try to figure out like okay give me all of the between three and five length words and you sort of have like this sliding window where you check each of the words against um against the uh the keys that are in word to digit but I think this is cleaner just even though it&#39;s using regular Expressions which is kind of hacky and isn&#39;t going to go very far it feels like a good enough solution for day one so thanks so much for watching and we&#39;ll see you in the next one

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