--- title: more pattern matching - Advent of Code Day 7 with Ruby slug: more-pattern-matching-advent-of-code-day-7-with-ruby published_at: 2022-12-08 00:00:11 +0000 updated_at: 2026-03-04 20:15:10 +0000 summary: description: more pattern matching - Advent of Code Day 7 with Ruby Challenge: https://adventofcode.com/2022/day/7 Solution: https://gist.github.com/cjavdev/a8122973da3303d76a93aeb614d6eff4 #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 7, advent of code ruby] views: 563 author: CJ Avilla url: https://www.cjav.dev/videos/more-pattern-matching-advent-of-code-day-7-with-ruby youtube_url: https://www.youtube.com/watch?v=cTDs-pmxHYU youtube_id: cTDs-pmxHYU embed_url: https://www.youtube.com/embed/cTDs-pmxHYU thumbnail_url: https://i.ytimg.com/vi/cTDs-pmxHYU/hqdefault.jpg type: video --- # more pattern matching - Advent of Code Day 7 with Ruby *Published: December 08, 2022* *Views: 563* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=cTDs-pmxHYU) [![more pattern matching - Advent of Code Day 7 with Ruby](https://i.ytimg.com/vi/cTDs-pmxHYU/hqdefault.jpg)](https://www.youtube.com/watch?v=cTDs-pmxHYU) ## Description more pattern matching - Advent of Code Day 7 with Ruby Challenge: https://adventofcode.com/2022/day/7 Solution: https://gist.github.com/cjavdev/a8122973da3303d76a93aeb614d6eff4 #ruby #adventofcode ## Transcript foreign what's up welcome back in this episode you're going to learn how to solve day seven of the Advent of code 2022 with Ruby this one is called no space left on device and it's all about sort of taking in some commands and looking at some files and looking at some directories and building up um this concept of a file structure so you can look at your file system and complete successfully this system update which right now is failing because there's no space left on the device so I don't we've all done this right like you want to go download some big file and from some really legit site and it's there's not enough space on your machine and so you have to like go and find which files you want to delete so today's problem is like okay let's take in this list of commands so CD for change directory LS for list files and then that's going to show us this output that tells us okay there's a directory inside of the root and inside of the root there's also two files one's called B dot text the other is called C dot debt and this is like the size or like the length of those files what we need to do is figure out how much or how big all of the different directories are and that means that if we're looking at the root directory that's going to be the sizes of all the files in all uh inside of the root directory but also inside of all of the subdirectories of the root directory so what we're going to do is copy this input here and we're going to just open up a new file for day seven all right so we're going to drop in our example input here at the bottom the input is either going to be a command that's starting with the dollar sign this is supposed to be kind of like your prompt and then so it'll be like a prompt then a space then a command then a space and then some arguments and in the case of Ls there's no arguments and when you run LS that's going to list out the files that are inside of that directory and so we're going to either get a something that starts with dur and then a space and then the directory name or we're going to get some number and then a space and then the file name and so what I want to do is I'm going to use pattern matching again in Ruby so pattern matching to the rescue I'm having a lot of fun just like playing around pattern matching and learning it and so what I want to do is I'm just going to like Loop over all of the lines that are here and start by pattern matching and saying like Okay this means we're going to change to a directory this means we're going to list files this means we're encountering a directory this means we're encountering a file I think those are the only four cases so it should be pretty straightforward so we're going to say something like data is data dot read lines and we'll say data Dot map Chomp which we do on every time we're reading a bunch of lines and now for each of these lines what I want to do is split on the space so that we have kind of like an array that has dollar sign then CD and then slash so I'm going to say map um again and here I'm going to map on the map and split on space okay that should give us an array of all these different things why don't we just also save this into some results and we'll print out results as we're working through this so we'll say Ruby 7 day 7. so that gave us what we wanted right we have an array with an array for each entry or each line and this first one is dollar sign CD and then some directory name so here what I want to do is say something like Dot each do line and then we're going to say case the case for the line and for now we know that we want to match on something that has a dollar sign and then something that has a CD and then something that has some like directory name and so we'll just say puts you know like changing into dur and then if we run this again what do we get changing into slash changing into a changing into e changing into dot dot so dot dot is sort of a special case that means we're going up a directory so let's actually add a special case before we get to this more General case and that is going to be jot dot dot and we'll say something like puts going up a level that way we can see what's going on here so we're changing into the root then a then e then we're going up a level going up a level then changing into D so this is going to let us sort of navigate around the the file structure and what I mean by navigate around is sort of just keeping track of the current path like you can kind of see here in my prompt I have this tilde that means starting from my home and then slash repos slash AOC and if I CD into day seven that pushes day seven onto this stack of directories that I that will like give me the current directory so if I do PWD that prints out my current working directory right and so here what I want to do is say like CWD maybe and that'll be a an empty array to start and if we go into a directory we're going to say CWD we're going to push that directory name in otherwise if we're going up a directory we're going to pop off of that right so if I do CD dot dot that removes day seven from my current working directory and I'm going up a level so that'll allow us to navigate around all right so we need some more cases here though in the case of Ls there's not going to be any directory here I'm just going to say puts like listing files or something I don't know like I'm not sure we even need that but whatever okay so we're changing into this directory we're listing some files we're changing into that directory listing some more files all right now we need to consider the case where we are actually looking at like the size and the file name so let's say puts like encountered um file name file with size whatever so we'll print that out so now we uh we see here okay we encountered file a with size dur uh oh so if it's a dur then we actually want to do something different so we'll again add another more specific case here dur this is gonna be like the dur name or something I don't know puts uh encountered directory with the dur name okay all right so we encountered directory a and then we encountered file B with size blah blah okay and then we encountered another directory and so what I think we can do is for now um if I remove the else that will raise an exception if we don't have any matches so I think we're good um just to confirm that is the case um no matching pattern error is the exception that's raised if you don't have an else block and you also don't have a match so here we're sort of matching we're matching everything or like all of the possible inputs at least based on the sample input so we've got some results and our results are well like our results actually don't matter and we're not actually using these for anything right now instead what we're doing is we're each we're using each to iterate over each line and then like modify this current working directory but we also need to sort of keep track of the size of the file so I'm going to like remove the print statements from our navigation so from pushing and popping and then what I'm going to do is I'm gonna We I don't think we actually need any we don't need to do anything in the case of listing files or working with directories instead what we care a lot about is this size here and some file name and so every time we encounter a file we need to keep track of its size and we also need to add that size to the current working directory but also like the size of any file impacts the size of its parent and its parents parent and so on anytime we're keeping count or like sort of a histogram of anything we can use a hash with default value so here what I think we want to do is say something like dur sizes is going to be a hash that every time we encounter a new key we're going to set the value to zero that way we can like easily increment it and here if we just did like dur sizes at the current working directory plus equal size then what would we get would be day seven okay and then we actually don't want to print that out we want to print out Dura sizes so P dur sizes okay so now we have the root and D root and D root and D that huh okay so I wonder if we actually want currentworkingdirectory dot dupe so that because right now it looks like even though we're modifying the current working directory it's showing us like the last the last one that it had okay so here we go so the root is pointing at this value slash a is pointing at this value slash a slash e is pointing at this value okay so I think these actually might map to what we have in the example right so total size of directory e is 584. 584 that's right total size of directory a is ninety four thousand eight oh okay ninety four thousand eight this should be an eight so what we need to do now is we need to add the value of the file e to a so rather than just adding the size here we need to iterate over currentworkingdirectory dot length dot times do like X or something and we need the current working directory from like 0 to X and we need to add the size to that I think maybe we need to also dupe this I don't know maybe using the slice operator will give us a dupe let's see okay there we go so now this has ninety four thousand eight fifty three so that subtle change was that like we went from just adding the files in the directory itself to adding the file to itself and its parent and its parents parent and so on and so forth up the chain so now we have okay so now we have this thing called directory sizes all right so now what we need to do is it says find all the directories with a total size of at most 100 000. so we need to iterate over dur sizes dot inject zero I don't know let's like try to figure out how to sum this up so we're going to say um yeah the so we're going to get a sum and then we're going to get the a directory and a size and we want to do some plus size if size is greater than oh at most is less than or equal to a hundred thousand undefined method Plus for nil class okay so is this what we're expecting p oh wait pea size okay that is the sizes oh you know what since we're doing inject we need okay we need to do like or so sum plus excess so if size is less than or equal to that then we need to do sum plus size otherwise we just do some okay so I think boom okay so this is 95 000 for blah blah blah okay so the total sum of their sizes is that okay so that is the answer for the test input for part one so now we need to grab our actual input so we're going to grab our puzzle input here and we're going to create a new file day 7 input paste it all in and then we need to modify our thing here so we're going to say like if arcv.empty otherwise we're going to say data is file dot read lines of RV at zero and okay so now we can say Ruby of day 7 input and we get back this giant number and let's see if that's the same boom okay so that is the answer for part one very cool um so again we gosh I love these pipeline things so here we are I mean we could probably do some even like fancier stuff with inject to like modify whatever but like this is fine we're like iterating over it and we're modifying this thing it's not immutable whatever it's not like you know this functional functional fanciness one Improvement we can make because we're not actually using this directory is we can just put like underscore there to ignore it and we should still get the same same result so that's kind of Handy if there's arguments to a block that you don't actually need you can use the underscore here we have to use these parentheses I think because yeah because we want to destructure that key value so the first argument to the block for inject is going to be our accumulator in this case the sum that's going to be default zero default set to zero so we're iterating over all of our our hat we're iterating over the hash right and as we're iterating we're keeping track of an accumulator that's our sum and every time we encounter a new element in the hash we're going to pass its key which we don't care about and we're throwing away with this underscore and the value which is the size that we stored up here and then this we're going to check to see if the size is less than a hundred thousand and if it is then we're gonna we're gonna add that to our accumulator and whatever's returned from the block that's going to be the next the next value of the accumulator for the next element as we go through this okay so let's take a look at part two all right we're now we're ready to choose a directory to delete the total disk space available on the file system is this so we have our total and to run the system update we need at least this so needed is this you need to find a directory that you can delete that will free up enough space to run the update so um what we like I guess taken is going to be der sizes of slash right like if we look at what is the total value of root that should give us how much is taken so so that's that is how much is free space so the free space is total minus how much is already used right okay so then what we need so delete at least is going to be needed minus the free space right there we go okay so that tells us how much we need to delete at least now what we need to do is go through the directories and figure out which ones we need to delete so I think we want to sort the values um so yeah so let's go through like dursizes.values.sort dot find where the size is greater than delete at least let's see all right is that the one okay increasing the use space by that so the one that we delete is that one okay fantastic so let's run this against our input and we get this answer 942 okay so that is the answer for part two okay so we have this is the total space in the system this is how much we need for our update the total free space is like how much is on the entire disk minus how much is already used we figure out how much is used by just passing in the root directory and we get back how much is free now we in order to figure out like which directory we want to delete we want to delete the one directory that will give us enough free space to install the update and so to figure out that directory we need to figure out like um how much we need to delete so we need to delete at least how much space we need for the update minus how much space is left over and free because we didn't use it as part of our file structure already so what we're going to do is we're going to iterate over the sorted values the sorted sizes and find the first one that is greater than that value so find here well call the block until it returns true and then whatever the value is it will return that value and print it out so that's how we got the answer all right so this was a pretty fun pretty fun one the hardest part I think is probably like parsing the input into the right like tree structure and when I was first thinking about this initially I considered using like classes for the nodes and uh you know building up sort of like a tree structure and then I was like oh but wait the I want to try to use pattern matching again so let's um let's keep messing around with Ruby's pattern matching and uh yeah so we have like the most specific case at the top in which case we're popping out of the current working directory then we have a more generic cases as we go down and then ultimately like this was also kind of part of the problem which was making sure that we're building up and keeping track of the sizes of all the files for the like Leaf like the bottom most Leaf node directories and also propagating that all the way back up to the parent yeah again another like really fun use of just kind of like calling a bunch of methods on Ruby classes so thanks so much for watching if you're enjoying this go ahead and hit subscribe and will have a few more of these coming down the pipe thanks so much and we'll see you next time --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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