--- title: pattern matching - rock paper scissors - Advent of Code 2022 Day 2 with Ruby slug: pattern-matching-rock-paper-scissors-advent-of-code-2022-day-2-with-ruby published_at: 2022-12-03 23:46:16 +0000 updated_at: 2026-03-04 20:12:59 +0000 summary: description: Using pattern matching in ruby to solve the advent of code problem for day 2, 2022. Challenge: https://adventofcode.com/2022/day/2 Solution: https://gist.github.com/cjavdev/1c38250a552aecdfa1fb07f11b0c4bd9 #ruby #adventofcode tags: [cjav_dev, web development tutorials, web development for beginners, vim, ruby, advent of code, advent of code 2022, advent of code 2022 day 2, programming projects, pattern matching, advent of code tutorial, advent of code ruby, ruby solution, ruby tutorial, ruby tutorial 2022, aoc 2022, aoc 2022 ruby] views: 754 author: CJ Avilla url: https://www.cjav.dev/videos/pattern-matching-rock-paper-scissors-advent-of-code-2022-day-2-with-ruby youtube_url: https://www.youtube.com/watch?v=xYk_xxIp0u4 youtube_id: xYk_xxIp0u4 embed_url: https://www.youtube.com/embed/xYk_xxIp0u4 thumbnail_url: https://i.ytimg.com/vi/xYk_xxIp0u4/hqdefault.jpg type: video --- # pattern matching - rock paper scissors - Advent of Code 2022 Day 2 with Ruby *Published: December 03, 2022* *Views: 754* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=xYk_xxIp0u4) [![pattern matching - rock paper scissors - Advent of Code 2022 Day 2 with Ruby](https://i.ytimg.com/vi/xYk_xxIp0u4/hqdefault.jpg)](https://www.youtube.com/watch?v=xYk_xxIp0u4) ## Description Using pattern matching in ruby to solve the advent of code problem for day 2, 2022. Challenge: https://adventofcode.com/2022/day/2 Solution: https://gist.github.com/cjavdev/1c38250a552aecdfa1fb07f11b0c4bd9 #ruby #adventofcode ## Transcript what's up welcome back in this episode you're going to see how to solve day two of the Advent of code in 2022 this is rock paper scissors we're going to do this in Ruby today so the elves are going to have this big rock paper scissors competition and there's an elf that you've been helping out who is giving you this sort of sneaky strategy guide that will allow you to win the whole competition so the way that you get your input is going to have this two column list there's going to be a bunch of different rows and each row represents like a round or one hand of throwing rock paper scissors against some opponent now while the elf is explaining to you how to win they say the First Column is what your opponent is going to play a for rock B for paper and C for scissors so we have this a b c down here the second column the elf got cut off they had to get pulled away so they didn't tell us what the second column is and so we're just going to assume that the second column is X for rock y for paper and Z for scissors and that that's just like the approach that we're going to take for this first part one now there is a way that you figure out a total score for each round so you're going to get points whether you win or Draw and then if you lose you're going to get zero points you're also going to get points for what you throw so if you do a rock you're going to get one point paper you get two points or scissors you get three points so it's a combination of if you win and you throw scissors then you get the most points and if you lose and you throw a rock then you just get one point for winning you get six points draw you get three points losing you get zero points so here's some example input a y x bxcz so this is rock paper right they throw rock we throw paper that means we win so we're gonna get six points for winning and then because we threw paper we're also going to get two points so this is like in the first example we're expecting that we're gonna get a total score of eight for this one round of rock paper scissors in the second round they throw paper and we throw rock so they win and which case we're gonna lose so we get a like an outcome score of zero because we lost and then we only get one point because we threw Rock so the total for that second round is going to be one third round we're gonna get three points for the draw and three points for throwing scissors also don't throw scissors that's like dangerous you'll poke an eye out like the first thing that I would do in this case is anytime that I've implemented rock paper scissors it gets a little bit like confusing right what what is actually going on so what I want to do is I'm going to add R specs so that we can run some specs so I'm gonna say bundle and knit bundle add our spec we're just going to add the R spec gem to some gem file install that locally and then I'm going to make a new directory called day02 and actually yeah before we do that we'll do our spec Dash Dash and knit that's going to initialize our spec and give us some config and stuff then I'm going to make a new directory called day two what we'll do is inside of day two We'll add a new file called day2.rb and I'm actually just going to combine the implementation and the tests all in one file this is like a handy approach that I've used in like interviews and if you want to just write small scripts this can be handy so you can just require R spec slash auto run and that will make it so we can describe things right here just in line our spec.describe I don't know rock paper scissors and maybe we want to start off with a couple methods maybe we're just going to have it calculates the scope correctly and so maybe we we're going to talk about the score as some so we're going to expect that this there's some score method that's going to take in a and Y so a and Y was this this first round and maybe our score is going to be like the total score is going to be eight but let's say that because we're throwing a y which is paper so because we're throwing paper we should get two right and then maybe or maybe this is the result of a and Y is 2 and then the bonus or something of a and Y so like we get a we get a win bonus because we won that round so that's going to be six and then we're going to expect like the total of a and Y to equal eight so we should be able to run this test and this is going to give us like the this is like building assertions around the output for this first example where we have this first round of a and Y so let's run this we can just say Ruby day two and now we're it's saying there's undefined method result this is great so as we're iterating what we want to do is make the smallest change possible to our implementation that will change the output of the test so we're just going to say def result and we can say them me and then rerun our tests rerun our tests expected to but we got nil so in this case what we want to do is based on what we through we want to calculate what value the result should be so in this case because we threw paper we wanted to come back with a two so for y we want it to be 2 for X we want it to be 1 and for Z we want it to be three okay there is another feature of Ruby that we can use here is looking at the sort of like ASCII value for a given character so if we open up IRB here and just say that a is equal to X and we say a DOT ORD or is going to give us the ASCII integer value for the capital x character in this case it's 88. now if we change a to y and look at the ORD for y it's 89. so they're going to be in order and lowercase are going to have different values in uppercase so in this case what we want to do is we'll just like we know that we're going to get two points for y and one point for X so what I want to do is I think I'm just going to take whatever value is passed in as what I threw or whatever this me character is we want to subtract 87 from the org so we're going to say me dot ORD minus 87 and that should give us the correct result based on the ASCII value so we're going to exit here and rerun our tests okay great so the test changed undefined method bonus now for rock paper scissors I'm gonna say def bone of them me and now let's run this again and we expected six but we got nil technically what I should be doing is like we want to just make the smallest change possible is just type in six and then it's okay undefined method total that calculates the score def total them me and rerun this again it's going to come back nil but we expected 8 so we could put in 8 here and now the tests should pass okay so what we needed is we actually need another implementation here so we're going to just say okay if let's make a copy of this and let's look at our second example so B and X so let's change this to B and x and we'll change this to B and for B and X your opponent is going to choose B and we're going to choose Rock so because we chose Rock our result should be one and our bonus because we lost should be zero so the total should be one so now if we run our tests again now we definitely have a failure we expected zero but we got six for the bonus method so if we go up to our bonus method here this is where we actually need to do the meat and potatoes and figure out what our sort of score is going to be right so if we win we want six so how do we tell if we were going to win there's a couple different things we could do we could say oh if if like them is equal to e and me is equal to X then we want our zero right because if they if they threw paper and we threw rocks then we want to return zero but and then all I don't know let's see else if they through b and we threw y then we want to return three because that's a draw else if if they threw B and we through z then we want to do a six right because that's going to give us a win so in this case they threw paper we threw Rock so we lose this case they threw paper and we threw paper so it's a draw in this case they threw paper and we threw scissors and we cut their paper and so that's a win but we don't want to have to go through all the different cases here so instead what I want to do is use a relatively new feature of Ruby called pattern matching so we're going to say case of them me and if it's in like B X then we want to do zero if it's in b y we're going to do 3 if it's in bz we're going to do 6 and what we can do now is say actually we can just say otherwise we win so we're going to figure out all the cases where we lose all the cases where we draw so this is going to be like a and X right if we both throw rock we draw if we both throw a paper we draw if we both throw scissors we draw if we if they throw Rock and we throw uh we need to lose so if they're throwing a rock we need to throw scissors and then we lose and otherwise if they throw scissors and we throw paper we lose and then otherwise we get six back all right let's run it and see if we get the right answer okay expected one got eight for the total so now we need to fix our total method just to see if this is going to work so total is going to be something like result of them in me plus the bonus of them and me and we'll run this again and now we have two passing tests all right so that's good let's add in this last case just just in case also the other thing you'll notice is like repeating we're repeating ourselves a ton here and so what we can do is rather than typing all this out every single time we can do we can create a list that is a why and then we can have it do two six eight and then we can have B X 1 0 1. and what we can do is we can just each we can yeah we can each over this and then only implement this once and then we have like result of them me is gonna give us this result oh also we need to name these differently result bonus and total so this is going to give us bonus and total and then we can remove these tests and when we run this we cross our fingers and hope we got it right oh no we got it wrong okay oh because this should be another them me situation okay run it again all right three passing tests fantastic all right so now what we want to do is run it against our input at the bottom we'll just say Okay file dot read lines of ARG Vita first and each line is going to give us a round so then we want to what are we going to actually get from this so let's print out what we're going to get um so in day two input we want to drop in our test input so we go back to the go back to the puzzle get our puzzle input I'm going to copy everything from here drop it in and now we should be able to say something like Ruby day two with input and or day two slash input okay so this is our output we get tons and tons of output it's giving us the right input so each of the lines has a round we want to Chomp off the new line here and then we want to split it so that we get we want to split on space so that we get a bunch of individual rows so we're going to say dot map Chomp and then dot map for each line we want to split it so we're going to say underscore one dot split on the empty string and now we should get something else okay so now each row has this C and or like it has its combos so now for each of those what we want to do is map them and me to some total of them and me so we'll run that again and now we get a bunch of totals and finally we want to let's see back on the puzzle what would your total score be if everything goes exactly according to your strategy guide so we're hoping for one three two six eight so we want to do like dot sum and that should give us our answer here okay one three two six eight all right so that is a that is the right answer we're still getting a bunch of failures for our R spec output that's because we're like now reading files in the middle of this but we know that our tests are passing based on the example input and we know that this should actually work so one three two six eight fantastic so that is part one for rock paper scissors in part two the elf comes up to us and they're like oh actually the second column in the second column X means that you need to lose y means that you need to win or that you need to draw and Z means you need to win so it's actually not what we were expecting and so this output is not what we want instead what we want is a different mapping of it so instead of getting the instead of the second column being the shape that we're throwing the second column is whether or not we're going to win or lose or draw so what we need to do now is modify our solution so that it works for this new approach and so what I want to what I think I want to do is rather than changing the the current implementation what I want to do is just have like total two and that'll be the total for part two and we'll say them and me and now we're going to get the result of them and me plus the bonus of them in me and the difference is going to be that instead of me being the win or lose we need to sort of like translate what me actually means let's let's go down to the bottom we'll comment out our our file reading we'll comment back in our spec here and we're going to add another test so in this in the second example it gave us a bunch of new Solutions so in the first round the opponent is going to choose Rock we choose paper but the total should now be four so what we can do is we can do the same sort of situation but now we'll just use like the new totals so that we can play with this so in the Second Use case we get back one and the third use case seven so that should be our our totals and then we're just going to use total two as as the test so now we can say Ruby day one or day two okay there's no R spec because we commented this out all right let's run it again okay so now we're getting a bunch of Nils but we expected expected nil but got eight what is this oh you know what it's because we're still passing these around so now this should just be oops it should just be total up here okay try this again all right so now we're getting the old answers we're not getting the new answers and so that means that we need to modify the input so what's happening is they're telling us you need to win or lose or draw and so what I was thinking is we can translate from the X Y or Z into what we threw so this is actually the total total number two is actually going to be like result or like the yeah the outcome and what I want to do is translate the outcome into me basically a me value so then what we want to do is like me is equal to some new method that is like transform them and outcome into me and then we can use we can reuse the same logic so now we have this this new function called transform this is not how I solved it the first time so this is going to be interesting how we look at this so if they if the outcome was okay so now I think we need something similar to what we had above so it's going to be something like if if they threw Rock and we threw scissors What should we return if they threw Rock and we threw scissors What should we return so let's let's do this let's do this thing again here or no if they threw Rock and we need to lose or win all right let's see X means that you need to lose so X means you need to lose so if they threw Rock and we need to lose so if they threw Rock and we need to lose that's going to crush scissors so we actually need to in this case return Z and if they threw Rock and we through paper or no if they threw Rock and we need to draw then we need to throw our rock also so that's going to be an X and if they threw Rock and we threw scissors no if they threw Rock and we need to win then we need to throw a paper so that's going to be why okay okay so once we've got like all of these patterns mapped out one thing we can do is just kind of like organize them so they're in the same spot so like I can put all the X's together so let's grab all of the X's here and then we can grab all the Z's and put them at the bottom and okay and we can grab the Y's and put them together so now we have XXX yyzz that should be so there's like all of these different patterns that start to to line up when you're working through these things and so what we want to do is actually just put all the X stuff on one line and then we can replace this with a pipe put all the Y stuff on one line and replace this with a pipe so pattern matching pattern matching in Ruby is pretty fun to play around with and then in fact like for these ones we can actually just change this to an else because we shouldn't get any other and like any other answer there right so let's run this again undefined local variable or method me for R spec calculates the score blah blah blah okay so where is it seeing me oh there is no me here this is outcome okay let's try this again all right tests are passing fantastic we'll come down here and comment this back in and we're going to switch this to Total two and that's going to be our part two answer and we'll comment out all of our R-Spec fun and run this with our A2 input and we get 15 508 15508 boom all right so that is the solution to day two in Ruby there's a couple of fun things we did in this version so using using pattern matching in Ruby again this is like super fun stuff right so yeah you can you can you can use these case statements and match on patterns we're only really using maybe like this pipe operator in an interesting way in this case but you can see how it would simplify maybe this humongous nested if else statement there's probably other really clever ways to do this this was like the the way that I wanted to do it so that I could play around with pattern matching so hopefully this was interesting or useful thanks so much for watching again if you're enjoying this Advent of Code season and if you want to learn Ruby obviously I'm gonna be continuing to make these so go ahead and subscribe to the channel if you haven't already alright and uh yeah hope you have a good day see ya foreign --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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