---
title: Tetris (kinda) - Advent of Code 2022 Day 17 with Ruby
slug: tetris-kinda-advent-of-code-2022-day-17-with-ruby
published_at: 2022-12-20 00:30:11 +0000
updated_at: 2026-03-04 20:15:14 +0000
summary: 
description: Tetris (kinda)  - Advent of Code 2022 Day 17 with Ruby  Challenge: https://adventofcode.com/2022/day/17 Solution: https://gist.github.com/cjavdev/1b9d1f89629c400f1c10ba05e8433c26  #ruby #adventofcode
tags: [cjav_dev, web development tutorials, web development for beginners, vim, ruby, advent of code, advent of code with ruby, advent of code 2022, advent of code 2022 day 17, ruby solution, ruby tutorial, pyroclastic flow, graph]
views: 384
author: CJ Avilla
url: https://www.cjav.dev/videos/tetris-kinda-advent-of-code-2022-day-17-with-ruby
youtube_url: https://www.youtube.com/watch?v=ZphG9VXELbc
youtube_id: ZphG9VXELbc
embed_url: https://www.youtube.com/embed/ZphG9VXELbc
thumbnail_url: https://i.ytimg.com/vi/ZphG9VXELbc/hqdefault.jpg
type: video
---

# Tetris (kinda) - Advent of Code 2022 Day 17 with Ruby

*Published: December 20, 2022*
*Views: 384*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=ZphG9VXELbc)

[![Tetris (kinda) - Advent of Code 2022 Day 17 with Ruby](https://i.ytimg.com/vi/ZphG9VXELbc/hqdefault.jpg)](https://www.youtube.com/watch?v=ZphG9VXELbc)

## Description

Tetris (kinda)  - Advent of Code 2022 Day 17 with Ruby

Challenge: https://adventofcode.com/2022/day/17
Solution: https://gist.github.com/cjavdev/1b9d1f89629c400f1c10ba05e8433c26

#ruby #adventofcode

## Transcript

what's up welcome back to the Advent of code series with Ruby in today's episode we're going to talk about day 17 part one this is actually very much like Tetris we're inside of a cave and there's rocks that are falling down and they are of these different shapes where we'll have what I call a dash plus a j a line and a square each of those are going to fall down and we're going to get some input that looks like this and this input represents some jets that are shooting some gases left and right and that'll make the pieces move left and right on the board as they're falling down and I think this is this is actually like a pretty fun exercise to go Implement just to go Implement Tetris let's jump into it okay we'll just grab this test pattern here and we'll say pattern is equal to this thing and now what we need to do is create a way to keep track of these pieces as they're falling down and so I did this with a class called piece and one of the things that I was doing was creating these class methods that would generate a piece of a certain shape so here I wanted to have self dot dash or something and this would give me back a new piece oh my gosh I was almost writing JavaScript for a second we're gonna we're gonna get back a new piece and that piece is going to have a certain shape so let's now the shape is going to represent where on the board it should be like filled in so for a dash it's like zero zero zero one zero two zero three and so here we get like zero zero zero one zero two and so on and then I can make an initialize method here that takes in the shape or the positions or whatever and then we store that off into the shape and now we have we have a concept of a piece right that is going to give us back a dash now another thing that's important is as these pieces are falling down we want them to enter or start on the board at a certain point and so in the instructions here the rocks are going to fall in order it's going to be the dash and then the plus and so on and so forth each rock appears so that its left Edge is two units away from the left wall and its bottom Edge is three units above the highest Rock so its bottom Edge is okay so then what we're also probably going to receive here is some like start point and we'll pass that down so that when we initialize our shape it has its X and Y coordinates are moved based on the start point so the start X and Y okay so that's going to give us our shape and so far we've said Dash but we also need all four other shapes and so I'm actually just going to copy and paste those in so that you don't have to watch me type them out Okay so we've got line Dash Square plus and we have line Dash square plus J and that should be it okay now what we want to do is we want to emit those shapes in order one two three four five right so we want to emit those in order so what I'm going to do is create a constant in this class which just has the symbols for the kinds of shapes so it'll be line Dash Square line oh that's that's wrong so it should be line Plus then J then oh wait no dash Dash then line then Square okay so given this array that is the order in which the pieces are going to be generated another thing that I want to do here is include the kind of piece it is so now done in our initialize method we'll take in the state the shape the start point and the kind and we'll store that in the in an instance variable here called kind all right so this is our initialize method and we should get back shapes like this so if I were to say IRB require day 17. RB now if I say peace.line I should get back a piece oh it's expecting a starting position so actually let's put it at 1-1 and so we got back a piece it is a line and its shape is one one two one three one four one okay so that gives us a Lineback if we say Dash at 1 1 we get a different shape right so this is now a dash now but what I want to do is to make sure that these always come out in order is create a class method called order and here we're going to use in this will give us back an enumerator so we're going to store off order it's going to equal order Dot cycle so now if we reload this we can say piece.order and that's going to give us back this enumerator that's called order and now we can say dot next and that will give us the next type of piece that should be generated and they're going to be in order every time we can also say order.peak and that will tell us what the next one is going to be so Peak doesn't actually like move to the next index in the array it just tells us what the current like next value is when we say next that will actually Advance it so here we see plus we were peaking a bunch of times we saw plus plus plus now when we say next we get the value out of it so if we say next again now we get J so what's cool about this cycle method on innumerable is that lets us kind of like go through the array over and over and over we don't have to do any modulo math or anything and we get back the pieces in order now what I want to do is say def generate or self.generate and here I want create a new piece based on the next piece in order so I'm going to take in a start point and here we're going to call send and we're going to pass in order.next because order.next will give us the symbol value for the next piece in the order and then we want to pass in the start point and we should get back a bunch of pieces so now if we call piece.generate that is seeing the dash and it's generating a dash for us now if we say generate again piece.generate again we're going to get back a different kind of piece so now we're getting a plus so that's putting it at the right spot Etc so what's really cool is now we are using this cycle we're using some meta programming with send and we're able to like generate pieces every time in order and they're going to be the right types at the right points okay let's add some methods so that we can move left and move right so let's say move left is going to be this new method that will create a new shape from our current shape so this is actually going to be we want y to decrease that'll move us to the left and we similarly want we want basically the same exact thing for right except we're going to increase y by one and now when we go down move down we're going to do the same thing except this time we want to increase or we're going to decrease X by one to move down now in each of these cases we can't move to the left if we're up against the left wall so we're going to return if y is less than or equal to zero and here we're going to return if Y is greater than or equal to 6. so for the problem the the grid is always at most seven wide and finally to move down we will return if x is less than or equal to zero and we also want to figure out how not to encounter another piece as we're falling down it turns out we'll have to do that the same thing for move left and move right but we'll tackle that in a little bit now the next thing we want to do is create a some sort of Grid or the tower a class for that so we'll call it class Tower our Tower will ultimately keep track of our grid and where pieces are on the grid so initially when we drop a piece at the top we'll have some current piece that is falling down for each tick and then we will also have the tower keep track of the instructions and make sure that we're like moving left or moving right and we can also use the tower to track the height of the of the tower which is what we're looking for at the end so what we'll we'll initialize with some instructions and here again we will use instructions dot cycle to give us to give us a way to iterate through several instructions or like loop around the instructions right because the pattern looks like this and so our instructions are actually going to be something like pattern.chars.map do c yeah if the C is the right arrow then move otherwise move left okay and then we're going to create a tower by initializing it with the instructions for the given pattern and now we want to say something like Tower dot height and that should give us how tall it is right now but because we haven't actually dropped any pieces we don't know anything else beyond that all right so let's let's look at the instructions again here so after a rock appears it alternates between being pushed by a jet of hot gas one unit then falling down one unit so we are either going left or right or we're going down and so we'll maybe we'll start off with falling is false and we'll say if we're falling we want the current piece some current piece at current piece to move down otherwise we want the current piece to follow whatever instruction is next so we can call currentps.sendinstructions.next and because instructions again recall that this these instructions are going to cycle through so we should get this giant list of move left and move right and every time we call next that will just give us the next one and if we complete all the instructions in the list it'll start back over at the beginning so as we step if we're falling we're going to move down and then we'll say falling equals not falling and same thing for if we are falling now if any movement would cause part of the rock to move into the Wall's floor or an or a stopped Rock the movement instead does not occur this means that we have to figure out how to tell whether or not we have reached the bottom reached a wall or reached another rock and so as we're moving down we need to give it sort of the current the current positions or like the yeah the current positions and so we'll make a new method here called current positions and what I think we need to do is also keep track of all of the like locked pieces maybe or something or maybe a grid yeah so we'll create a grid that is full of zeros this one is a 7x7 grid full of zeros and we also want to keep track of the pieces and the current position is going to be at pieces.map or flat map the shape so that should give us all of the positions that a piece covers when we get to step we're saying current piece that moved down but we don't actually have a current piece yet so we need to First spawn a piece if there's no current piece how do we spawn a piece we're going to say the current piece is going to be a generated piece and we're going to generate it at 0 2 or the top I guess we want this to be at the height of the grid so at grid.length minus one or something so we'll generate at acrid length minus 1 2 and then we're going to step and when we step if we don't have a current piece we're going to spawn one and if we're falling then we're going to move down if we're not falling we're going to move the piece based on the Jets and then eventually we're going to hit the bottom let's also make a way to print out the tower okay let's see how this works tower.tick or step let's have it step a few times and then we'll put s tower all right Ruby day 17 okay undefined local variable or method y for peace yes so return if Y is less than zero so this is actually going to be like return if at shape dot any of we don't care slash why if any of them are less than or or equal to zero we want to return early same thing with move right if they are greater than or equal to six and four move down in this case we care about the X but not the Y if the x is less than or equal to zero we can't move down anymore okay so now we're getting the wrong number of arguments for move down okay so now we're we're taking in the yeah the positions and similarly we want to return if modifying the shape would have it interfere or overlap with an existing position do any of the current positions X Y would any of the current positions X values or XY values match PX minus 1 and P Y yeah p y okay so this yes so this should work okay and we'll run this okay so now P tower.height Tower doesn't have a height so we'll make a new method here and we're going to go through all the current positions map the first one and get the max that should give us a height value okay so we get nil back and we are printing out something it looks like yeah it looks like we're we're seeing something here yeah so we actually want to go over the Grid in a different way we want to go over the grid so that we can get I and J out we want the zeroth row we want the bottom row to appear last when we're printing it out so we want to print the top row of the grid first so we're going to start with grid.length and we'll go down to zero or yeah down to zero and that's going to be our X and this actually might have to be grid.length minus one and then we need our Y which will be 0 to 6. each do y and then if the current ends include X and Y put a pound sign else if current piece and the current pieces shape includes X Y then we're going to put an at sign this is just so that it matches what's in the example and then we're going to join and then that I don't know let's see how that looks current piece.shape is not exposed so let's make this add a reader for the shape all right join oh this should be map okay we got a tower back dot join okay so now we're not doing new lines all right here is our piece our current piece that's falling fantastic all right so what we want is we want like every time we step we want to see if the piece is actually moving down or not okay so when we started the piece was at the very top then it moved down then it moved down then it moved down and then it stopped okay all right let's clean this up so it's a little bit easier to play around with okay all right so let's see here what we get okay so after 10 steps we're starting to go back across the board there and okay so we started we started very very high and we're continuing to work our way down so what I want to do now is instead of starting the array at seven I'm going to start this at four we're gonna make it four tall and seven wide and let's see what happens here okay so now if we look we start and the top we're going okay so this is actually too far to the right so we actually want it to start here this should actually I think be one because we want it to spawn yeah we want to spawn exactly two from the from the left okay so we're spawning in the right place and then we're falling down one and then we're being pushed to the right one but I think if we look at the instructions here the first rock begins falling but then it encounters a jet of gas first so it should have it should have handled move right first so if we're falling we should not be falling so falling is false so we spawned a piece and we're not falling so then it should have gone to the right so after this very first step I would have expected this to move just to the right but not down but it went to the it went down first and then to the right we need to figure out or fix our order of operations here let's give some debugging here we're going to say puts let's push the Rock and then we'll say instructions remember we want to use Peak not next because Peak is going to allow us to look at what the next value is without actually pulling it off and cycling so here we're just saying Peak and then otherwise we want to say puts falling down and let's see what we get here okay so we start off at the top Jets push move right oh you know what okay this is because I started this at the wrong spot so that it is supposed to be two but we just didn't we didn't see the tower when it was first created or we didn't see it when we first spawned the piece okay all right so the Jets push and move the move the piece to the right okay so it started here but then after our first move we moved it here and then we printed out the board okay great and then we fall down and then we try to push right again but nothing happens because we're at the wall and then we fall down again and then a jet pushes us right and nothing happens so then we fall down again and then a jet pushes us left and then we fall down again but we can't move anymore so we should lock in place here if we if we attempt to move down but we can't move down we should lock in place here where we go to move down instead of moving down we want to lock in place in order to know whether or not we land on top of another piece or we reach the bottom I won't move down to return true or false so I'm just going to say if we couldn't move down then we want to lock the piece current piece and then we're going to set current piece equal to nil and that should respawn the next time we go so what does lock piece mean lock piece this means that we're going to say we want to add that piece now to our list of pieces and we also want to go through each of the X Y coordinates and set those equal to one on our grid so that we can no longer go to those positions and when we print it out we should print out the like pound signs so let's run this again all right all right after we moved left back to this position we tried falling down once more and then we locked in place so now we have those four pound signs cool now the next Rock begins falling and that's a plus and the bottom of the plus is above like the second pound sign and so we see something starting to show up here but we don't actually see the whole piece up here and we do see the piece continuing to fall down but I think when the piece was spawned it wasn't in the right spot so one thing we can do is where we're spawning the piece we could just print put spawning piece and its type currentpiece dot kind and then we'll also put self just so we can see what the board looks like at that point and current piece is it not called kind or we don't have a reader for that yet okay so here we are we're spawning the piece plus and its bottom is Right Above This pound sign here so that is going to come down into the right position so the next step it looks like it got pushed to the left and it did and then it falls one unit and then it gets pushed to the right and then it falls one unit and then it pushes to the left Falls one unit pushes to the right ultimately settles like this so let's make our test Runner run I don't know 20 times now and we'll see where we end up okay so it did not end up in the right spot right so like right above it should have locked in place right above the second pound sign and it locked above the first pound sign so something is wrong with our like locking in Pace in place so is starting okay so it's actually starting too close so right here we have one two there's only two rows between where the piece was spawned and we actually need three rows so in order to figure this out now what we need to do is go back to our our spawn piece method here and instead of grid.length minus 1 what I want to do is have it spawn exactly three rows above the max height so we're going to say height plus 3 and that should get us a little bit closer let's add some more debugging here we're going to spawn the current piece at height plus three comma two all right so for our height which is being used to calculate where we're going to spawn the next piece we actually want this to be current positions Max plus one or zero so what I'm actually going to do is say if there's any current positions then we will do this else we'll just say like zero that way we don't get a nil a nil error for Max not having something and now we'll run this okay current positions dot any let's make sure that we're dropping in the right place so we should be spawning a piece at four two we are that's perfect okay because now we have three empty rows between where the piece was spawned and the the bottom okay we're gonna push left we're gonna fall down we're gonna push right we're going to fall down we're moving left we're falling down we're pushing right we're falling down and that locks it in place correctly right above the second pound sign there okay and then the next rock falls and that's going to be a j and the J so this then like the the text of the answer just tell us what it looks like after a piece is spawned every time and then let's say that we actually want to step like a hundred times and we'll run this and see what happens undefined method square bracket equals for nil class on line 118. so when it's going to lock a piece in place after we grow to a certain height it can't lock it in place above the top of the row right so this it's trying to spawn a piece at 12 2 but it can't fit something above this right or it's trying to spawn something above this so every time we add a piece we want to check and make sure there's enough space to add that piece so as we're spawning a piece here let's check to see if grid.length is less than height plus four then we'll say at grid plus equals array that is seven wide and has all zeros so we'll add four more rows to it let's see if that gets us further okay I think we're getting the same error but yeah so we need to add maybe we need to add seven of these let's see oh dot new array.new all right so now we can see all of the different spawn points okay let's see here so it's spawned the J then the next one was it spawned a line that was right then it should have spawned a square that looks right and then when it spawned the square it looks like it should have been in a different form though right like it should have been a different shape when it when it ultimately spawned the square so we have we have another bug in here somewhere so our height is correct we're generating the right pieces we're generating them in the right order we're adding rows to the top let's actually make this the height plus seven okay so the other the other thing that's happening here is that as the pieces are falling down they're they're crashing into each other and starting to overlap each other because we added this condition for move down but we didn't add it for the others and that was we want to make sure that the even if we attempt to move right which is going to be y plus one if we attempt to move right we want to make sure that there's no pieces that are already covered by that so we need to pass in positions like the current the currently taken positions and we'll add another check here for that same thing and this is going to be okay so there all right now we're seeing wrong number of arguments that's because when we when we ultimately call send with our instruction we need to now include our current positions okay all right now when this piece is falling it wait is that the right one okay we're coming up a little bit all right so when the square starts to fall this is the shape we expect when the square first starts to fall this is the shape we expect then we get a line and it looks like this then we get a plus and it looks like that that looks right just like this top level thing all right and then a j starts to fall like that okay you know what we've got it we've got it solved so now pieces are falling in the right order in the right places and now it's just a matter of solving the problem which is to figure out the height after a certain number of rocks fall so to prove the elephants in your simulation are accurate we want to see how tall the tower will get after 2022 rocks have fallen so we need to keep track somehow of some like number of rocks inside of our Tower so we'll go up to our Tower and our instructions are now going to keep like some piece count and we'll say at peace count after 2022 rocks have stopped but before the 223rd Rock begins falling so every time we spawn a piece we should check to see if the piece count um yeah we'll just say piece count minus equals one if the piece count is less than zero then we're going to throw throw done and we'll just actually yeah we'll throw done and we'll also like put like current height is height and then we'll run this nope we want to now just tick until it throws so we're just going to say while true Tower dot tick or tower.step or whatever we want to keep going until we received this throw you can take out some of these print statements oops we want to keep that one okay we don't need to know if it's falling down anymore or if it's pushing it anymore all right let's run this again let's also run we'll just like print out piece count just so that we know that we're actually like falling down Okay cool so now we just wait till we get to the bottom of this number and that should tell us how tall the Tower is so this is the count of rocks that are falling and they're stacking on top of each other and the tower is getting super big because 2000 22 rocks quite a few rocks boom okay current hit current height is 3068 which is the right answer for part one and that is it so I thought this was a pretty fun pretty fun little exercise and it allowed us to use cycle and innumerables again to generate a series of pieces I fully expected part two to be like okay we're gonna now rotate the pieces as they're falling so that we could really simulate an example of Tetris I think this is also a pretty good starting point for implementing Tetris I'm excited to go use some of the same logic to implement Tetris with dragon Ruby but that's what we're gonna leave it today this was a super long one so we're just going to cut it short by solving part one part two is the basically the same thing with a little bit of math so you're gonna find some height like the find a cycle that's going to repeat calculate the height of that and then multiply out until you get to a billion or a trillion tall or something so that is the end of day 17. thank you so much for watching really appreciate your time and attention and we'll see you in the next one cheers

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