---
title: Grid of Characters - Day 03 - Advent of Code 2023
slug: grid-of-characters-day-03-advent-of-code-2023
published_at: 2023-12-03 16:00:09 +0000
updated_at: 2026-03-04 20:15:19 +0000
summary: 
description: Let’s solve the Advent of Code 2023 Day 3 puzzle in Ruby! In this video, we'll parse a text file representing a gear assembly schematic. We aim to sum the values of all numbers adjacent to marker symbols.  First, we'll break the input into rows and iterate through, identifying symbol locations. Then for each symbol, we'll search neighboring cells for adjacent numbers. By traversing left, we can find the starting digit to extract the full number value.  For part two, we'll adapt our solution to only consider star symbols with exactly two adjacent numbers - representing gear ratios. We'll get the product of these number pairs and sum the ratios.  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, rails, advent of code, advent of code 2023, advent of code with ruby, advent of code ruby, advent of code day 3, day 3 2023, aoc 2023, advent of code 2023 ruby, string range]
views: 514
author: CJ Avilla
url: https://www.cjav.dev/videos/grid-of-characters-day-03-advent-of-code-2023
youtube_url: https://www.youtube.com/watch?v=H32Od3uZEs4
youtube_id: H32Od3uZEs4
embed_url: https://www.youtube.com/embed/H32Od3uZEs4
thumbnail_url: https://i.ytimg.com/vi/H32Od3uZEs4/hqdefault.jpg
type: video
---

# Grid of Characters - Day 03 - Advent of Code 2023

*Published: December 03, 2023*
*Views: 514*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=H32Od3uZEs4)

[![Grid of Characters - Day 03 - Advent of Code 2023](https://i.ytimg.com/vi/H32Od3uZEs4/hqdefault.jpg)](https://www.youtube.com/watch?v=H32Od3uZEs4)

## Description

Let’s solve the Advent of Code 2023 Day 3 puzzle in Ruby! In this video, we'll parse a text file representing a gear assembly schematic. We aim to sum the values of all numbers adjacent to marker symbols.

First, we'll break the input into rows and iterate through, identifying symbol locations. Then for each symbol, we'll search neighboring cells for adjacent numbers. By traversing left, we can find the starting digit to extract the full number value.

For part two, we'll adapt our solution to only consider star symbols with exactly two adjacent numbers - representing gear ratios. We'll get the product of these number pairs and sum the ratios.

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

oh what's up welcome back in this episode we're solving day three of the event of code for 2023 this one is called gear ratios and you and the elf we got to a gondola lift and the gondola lift is going to take us up to some other station but the Gondola's broken down there's some issue with it and our input today is some engine schematic and we need to figure out something about all of these numbers anytime I see these in the Advent of code I know we're probably going to be doing something with this grid and that is the case here we have some symbols like the star the pound sign the plus the the asteris money sign and we've also got some numbers four five 6 7 and what we want to do is find out which numbers are adjacent to any symbol so here we have a star and next to the star right below it is a five and a seven is diagonally adjacent to the star and so that counts two this 114 the one is not actually diagonally adjacent to the star so that we would say that this number is not touching a symbol so what we need to do is go through and find all of the numbers that are adjacent to or touching a symbol and we're going to add those up and return the number and that is going to be the sum of all the parts in the engine and that's our that's our answer for part one so for this example input we're looking for 4361 let's just grab that example input crack open our terminal here drop that in and get to work the way that I thought about solving this was to break up each of these input lines into rows and then we can access characters in each row by index because we can index into a string so if we have the string ABC we can index into it at one and that gives us back B we're going to do that uh using yeah so for data actually we'll just call data rows this time and what we want to do is say like rows. each with index do row and that's going to give us the row index let's just call this X for now and then we can say Row for each character do y and the first thing that we want to do is just find where all the symbols are so we're just going to keep them this like list of like where all the symbols are so we'll just keep an array here and we'll say if the character or maybe like next if the character is the period and next if the character is a a digit and then otherwise we're going to pop that into the symbols here and we don't actually need the raw character so let's see if we can get all the locations for the symbols so we run this and we got 010 010 that looks wrong for sure maybe to help here what we can do is print out the character um yeah let's print Char and X and Y okay so that is all of uh this is symbols but it's also uh new line characters which we don't care about so before we even start messing around with rows let's map and Chomp those and here we go so now we're looking at symbol and then the location of the symbol my thought process is let's just find the locations of all the symbols and then we'll look at all of the adjacent spots around the symbol and if there's a number in that spot then we'll grow out in we'll go to the left until we hit either a DOT or the edge of the board and that will let us give us like the starting point of each number and we'll use the starting point to figure out what the number number is okay so now that we have each symbol we can say sims. each do X and Y and uh for each of those what we want to do is we want to go in every single direction we need to go back one and up one we need to go up one forward one and up one the way I typically do this on most of these grid problems is I'll make a list of -1 and then 1 0 1 1 01 yeah this list will generally let you iterate over a DX and Dy so that you can find all of the neighbors around this thing and if we find a number we're going to say that we like uh potentially have a a number location or something like that so maybe we say like number locations and here we'll say if rows at uh NX n y is a digit then we'll add that to our number locations so we want to actually add NX and Y and then at the end here we'll just p number locations and see what we get okay so we're seeing 02 22 so 02 would be 0 1 2 so that's seven that's right and then 2 2 so 0 1 2 012 that's this three that is correctly adjacent 2 3 35 is also adjacent 2 six 0 1 2 3 4 5 six okay so I think we are correctly finding the locations of numbers that are adjacent and we I yeah so let's like just to verify we should not have Z 1 two 3 4 5 0 five should should not be in this list and it looks like it is not there because that would mean that we are including 114 which is not adjacent to a symbol all right so now for each number location we need to figure out what the whole number is and when I was going through this I my thought was like it doesn't matter where we landed in the number if we just keep going to the left inside of that row until we either fall off the board or hit a DOT then we can find the index the Y value for the first or I guess it's X I don't know whatever like the index in the row for the first digit in each of these numbers and then we can use that to figure out what the number is what we want to do is for each of these number locations we want to say maybe like number starts like starting points for the numbers and we can say what we want to do is while rows of X and y- 1 is a digit decrement Y and then at the end number starts is going to be XY so this should give us doing this Yus equals 1 should let us shift over to the left until we get back to the beginning of any number so now if we print out number starts we should see okay so 0 0 22 and 22 ah we've got two of the same starts in here so that actually makes sense right so 0 0 that's correctly this one four and then we have 2 two which is three and we have that twice that's because both three and five are adjacent to this star and maybe one thing we could do is just make number starts set so that it's Unique set. new and in order to do that we have to require set set is a collection similar to an array but it will only allow unique elements so if we run this again now we have the set of 022 26 4 and so on also to make it a little easier I'm going to print the input so that we can see it while we're debugging here okay so 0 0 22 26 4 0 good 62 okay so that is looking really good so now we've got the locations of the number starts and in Ruby we can use indexing again into each of those rows based on the number start and then we can just convert it to integer because technically in Ruby if you have 1 two three and then some words which we will in the form of dots right if you convert this to I you get one two three because the string starts with a digit that can be converted into an integer and so we can take advant of this nicity of Ruby and if it starts with some dots what we can do is then just index into this from 0 1 to three with an infinite range so this will grab like from three to the end of the string and then we can convert that to integer so it's grab all these convert it to an integer and then if we need to get another number then we'll say grab all this and convert it to an integer it's and so on so we'll say number starts that each to XY and then we can say rows at X Y up to the end. 2i and I think this should maybe give us some uh some numbers we can play with so let's say let's just P result and see what we get all right so 467 35 633 617 those are all the numbers that we're seeing up here that are adjacent to symbols that's fantastic now in order to get our answer here we need to find the sum of all of those parts so we're just going to call do sum and run it and we get 4361 4361 is what we were looking for so now we want to try it against our puzzle input so we'll grab our puzzle input here and we'll drop it at the bottom and it looks like I've got an extra line there and then we can switch from from our example input to our data that's at the bottom of the file we run this and we get 527 369 okay boom that's part one that is our answer for part one all right so for part two all right let's look at the the question for part two so the engineer finds that the there's a missing part they install it blah blah blah we fixed part one for part two we're talking about gear ratios so the problem is going to shift here and and a gear is any star symbol that's adjacent to exactly two part numbers so we need to look for star symbols that have two numbers connected to them so right here 467 is connected to 35 with a star symbol so they only and this this symbol only has two numbers adjacent to it right it doesn't have one it doesn't have three here's another star symbol that has exactly two numbers adjacent to it so this is what we're looking for now we're looking for only the star symbols that have two two numbers adjacent and then that's going to give us a gear ratio and in the schematic a gear ratio is the two numbers that are adjacent to the star multiplied together so what we need to do is figure out 467 time 35 and that gives us the gear ratio for this top left group and then we're going to add that to the gear ratio for the bottom pair of numbers that's adjacent to a star all right so the problem shifts a little bit right instead of looking for all the symbols what I want to do now is just make it look for the star symbols and now we have to figure out how we're going to exclude the cases where we only have one number next to us right in when I was doing this I actually copied the entire thing because I didn't want to mess up the solution for the first one so here as we're going through and finding all the symbols what we want to do now is just add the symbol if the character is the star and the rest of this doesn't actually matter I don't think okay if we do this though oops let's run against our example input all right if we run against the example input now we get 0 022 that's correct but we also get this 4 Z so 0 1 2 3 4 4 Z so we're seeing 617 617 should not be included in our solution because this asteris only has one number adjacent to it so what we need to do is figure out how we can only include numbers that have or like number starts when the symbol has two numbers adjacent to it so rather than iterating over the symbols and collecting the number locations and then separately figuring out the starts and then separately like converting those uh into integers what I think we want to do is for each symbol we need to action each symbol right we can't do these all in separate steps anymore because each symbol now we need to know like how many adjacent numbers are there what we can do is move like most of this content inside of the block for each symbol so now as soon as we know the number locations for a given symbol we can iterate over that subset and I think yeah I think we might even want to create number locations inside of here so we're going to iterate over some set of number locations for a given symbol and when we encounter each one we're going to go back and find a number start and then if number starts. length is equal to two then we will figure out what the number is map it to integer inject to create the product and then we'll P the result and let's just see what we get here okay so now we're getting 45149 45149 0 okay that gives us the second gear ratio in 1 16345 1 16 345 is the first gear ratio so those are the two gear ratios that we want to add up so we're given back these gear ratios okay and yeah so maybe we can keep track of some like sum and we'll set that equal to zero and we'll do like sum plus equals result and then we'll just P sum at the end here and now we're getting 467 835 467 835 so that is that is the answer against the example input so now let's run it against the real input here 730 74886 730 4886 boom that is the answer for part two all right that was actually not that bad we've got a bit of a mess here just like print stop printing out the number starts and then yeah like anytime I do this sort of thing I don't know yeah there's probably better ways to iterate over the adjacent neighbors and figure out what their number locations are but this seems to work fine for now also these number starts now that we're inside of yeah even though we're inside of here we still need these number starts because we might end up um with multiple number locations that are going to that we need to count back from technically we could have moved a bunch of this stuff into here here let's actually let's try this so let's say that number starts is also up here okay all right it's still working okay so now what we want to do is try to try to iterate here so while rows at NX and nyus = 1 NX or n n y is equal to NY NN y NN y minus equals 1 and then we do like number starts as nnx minus NN y does this work okay okay nice all right with this solution we are able to iterate over the number locations and pull out the number starts like the unique number starts while we're iterating through the neighbors so this is a little bit better and yeah so if the length is two cool so this is probably as concise as I would want to go uh and yeah I'm pretty happy with this solution all right that's it thanks a ton for watching we'll see you in the next one

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