--- title: Range overlap and intersection - Day 05 - Advent of Code slug: range-overlap-and-intersection-day-05-advent-of-code published_at: 2023-12-05 23:30:06 +0000 updated_at: 2026-03-04 20:15:17 +0000 summary: description: In this episode, you’ll learn how to solve the tricky Day 5 advent of code challenge involving massive number ranges and mapping \"seeds\" to \"locations\". I parse the input data into seeds and conversion rule groups. Then build a find method to apply offsets from each group's ranges. For part 1, we'll traverse the groups to map a seed to its lowest possible location number. Part 2 requires handling seed ranges, so we create a convert method to break ranges into intersecting sub-ranges with offsets. By tracking these in a nested array, we cascade through each step without exploding memory. The core solution leverages custom range intersection and set logic to avoid iterating impossible quadrillions of numbers. We’ll change the Range object with monkey-patching to add overlaps? and intersection methods. 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, Learn to code, Beginner ruby, Advent of code, Advent of code 2023, Advent of code ruby, Aoc ruby, Aoc 2023, Vim, Advent of code vim, Advent of code explainer, Advent of code challenge, Code challenge, Advent of code tutorial, Web development tutorial, ruby range, ruby range intersection, ruby range overlaps] views: 454 author: CJ Avilla url: https://www.cjav.dev/videos/range-overlap-and-intersection-day-05-advent-of-code youtube_url: https://www.youtube.com/watch?v=VcYHkGgQPqs youtube_id: VcYHkGgQPqs embed_url: https://www.youtube.com/embed/VcYHkGgQPqs thumbnail_url: https://i.ytimg.com/vi/VcYHkGgQPqs/hqdefault.jpg type: video --- # Range overlap and intersection - Day 05 - Advent of Code *Published: December 05, 2023* *Views: 454* ## Watch [Watch on YouTube](https://www.youtube.com/watch?v=VcYHkGgQPqs) [![Range overlap and intersection - Day 05 - Advent of Code](https://i.ytimg.com/vi/VcYHkGgQPqs/hqdefault.jpg)](https://www.youtube.com/watch?v=VcYHkGgQPqs) ## Description In this episode, you’ll learn how to solve the tricky Day 5 advent of code challenge involving massive number ranges and mapping "seeds" to "locations". I parse the input data into seeds and conversion rule groups. Then build a find method to apply offsets from each group's ranges. For part 1, we'll traverse the groups to map a seed to its lowest possible location number. Part 2 requires handling seed ranges, so we create a convert method to break ranges into intersecting sub-ranges with offsets. By tracking these in a nested array, we cascade through each step without exploding memory. The core solution leverages custom range intersection and set logic to avoid iterating impossible quadrillions of numbers. We’ll change the Range object with monkey-patching to add overlaps? and intersection methods. 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's up welcome back in this episode we're doing day five of the event of code for 2023 we're going to talk a lot about ranges and man this one was a doozy this was tough this was super tough so this one's called if you give a seed a fertilizer it's If You Give a Mouse a Cookie type situation we have met a gardener who is helping us out and The Gardener has an almanac and they're having trouble making sense of this Almanac and I trust that most people who encountered this also had trouble making sense of it okay let's walk through what we've got here the top is a list of seeds and in part one each of these seeds is an individual number that we're going to count as a seed then we have a bunch of these Maps now the way that the maps work is they converting a seed number into a soil number so we are looking for how to convert that so our source category is in the middle our destination category is on the left and then the number on the far right is how far those ranges extend so in this case because we have a two for the length of the range our source goes from 98 to 99 and our destination goes from 50 to 51 and we need to figure out like if we're given a seed that is 98 it needs to map to a soil number that is equal to 50 similarly here our source starts at 50 and then it goes 48 numbers so 50 51 52 53 all the way up to 98 and those numbers map to 52 53 54 all the way up to 100 we need to figure out how to map from a seed all the way down to a location when I first saw this I thought oh this is going to be super cool because we can use zip so we could convert convert 98 into a range of 98 this plus this many and 50 into a range of 50 plus this many and then we could zip the two of them together and build a hash where we have a number on the left that points to a number on the right and then we could build up several of these different hashes Traverse these all of these dictionaries and get our number and then I looked at your puzzle input the puzzle input for today is these insanely massive numbers and the ranges that we're working with remember that the number on the far right this is the length of the range so for our source number here which looks like three billion something plus 7 million something right so if we were to do that with addictionary we would end up just with these huge massive dense dictionaries of numbers and so that's not going to work so we've got to figure out a more efficient way to do that so let's get started with this first part in part one we want to find the lowest location number that corresponds to any of these initial seeds so any of the initial seeds that are passed in we want to find what is the lowest location number that we can map to in the case of seed 79 it ends up with location 82 let's make our first goal just see if we can get from seed 79 to soil 81 with this with this input here so we've also got to do a bunch of parsing and some other stuff all right so let's at least get this parsed into a format that we think will work well for us so let's open up main. RB here we'll drop in our input we have this seeds business at the top and that's going to give us some numbers we want to work with and then the rest are separated by a an extra new line so let's start by grabbing off our seeds so we'll say input. split on on two new lines and and that should give us back our seeds line and then the rest of the lines P seeds May Ruby or B okay so then we're going to say seeds is equal to seeds. split on we can just split it and then dot map 2i and we can ignore the first one and bundle up the second one or like the rest of it and we should get this array of numbers does that not work oh uh seeds dosit map toi okay so now we have 794 55 cool so that gives us our seeds now let's work on the rest of these lines so now if we look at lines what is that okay seed to soil map and then these are all going to give us these rows of things for each I guess this is like a group groups so we will say groups is equal to groups. map and then we want to split on uh new line the first one is going to be the label and then the rest is like these mappings that we actually care about and we want to go through each mapping okay and let's print out groups to see what we get back all right so our groups look like this so one group has the array of 5098 and 2 5098 and 2 and again looking back at our goal here is we want to get from 79 to soil number 81 if we look at the difference between these the source and the destination we get like this offset let's reorganize this to also have we have the destination we have the source and then we have some length and what I think we want is we want the source we want the source plus the length and we want the destination minus the source to give us like some Delta so we want to take 50 minus 98 to know how far we need to shift from seed to soil when we encounter this mapping here so this DS minus Source should give us the destination um to Source Delta right okay so now let's P groups okay so now we have 98 100 so if our seed is between 98 and 100 then we need to apply this Delta to it to get out the soil version of that same if it's between 50 and 98 we need to apply this Delta to get the the soil version of that so now what I think we can do is let's just try with one seed and I'm also wondering if we want to just convert this into a range right now so if we run this then our first element is a range from 98 to 100 and it tells us the Delta and what that does is it makes it so that when we iterate over uh each of these groups we can find yeah we should be able to find which groups are applicable to our given seeds so if we say that seed is 79 we need to go through groups zero because we're we only care about the first group which is the seed to soil group and for each of those we want to see if that group range includes the seed so if the group range includes the seed then we want to if the group range includes the seed then we want to apply seed Plus or yeah plus offset that's what we want to like kind of print out and then we'll break so let's just see yeah so we get back 81 okay so 81 is the Delta or I'm sorry 81 is the soil number for seed number 79 does this work for 14 let's see 14 it does not so we got no output for 14 one of the other things that I forgot to mention was that if there is a range that is not covered by the mapping explicitly then we assume the Delta between the two is zero and that it's a direct mapping between the input and the output so so when we're looking at this C to soil here there's an invisible one that goes what the source is zero and the destination start is zero and the length is up to but not including the next like the first range so this would go like 49 I think and then similarly there is a an a range that goes from the highest Source all the way to like Infinity so in this case it's like a 100 or uh this would start at 100 100 and it would go like Infinity so there's like a start cap and an end cap to each of these ranges so we need to add those in so we can do that by um injecting something here within each mapping we want to sort the list of these rows so we I think for now yeah okay sort by range that should work let's see 50 to 98 0 to 15 to 52 okay those are sorted and then once they're sorted um okay we want to look at the first element okay the first element is the lowest range and then we want to look at the first element of that and it's begin okay so if this this does not equal zero then we want to add in mappings do unshift from that up to begin with that now if we P mappings yeah so now that matches okay Zer to 50 50 to 98 98 to 100 all of those look good and we have all of our zeros now what we want to do is add our end cap so now we want to say mappings do push okay let's just see if this worked as expected okay so now we have one from 98 to 100 100 to Infinity 52 to 54 54 to Infinity 53 11 53 53 to 61 61 to Infinity okay so now we should have good mappings and when we iterate over each of the grp groups we want to see if it's included in there okay so now we got for 14 what did we get back we got back 14 for 14 yeah its corresponding soil number is 14 because it's not covered by one of the ranges for uh seed to soil right so this should fall into the default range of 0 to 49 and the diff should be zero so that looks good so if we have a seed number of 55 the soil number should be 57 so let's add our seed number of 55 expecting 57 we got 57 great okay now that's working for seed to soil now we need to go from seed to location and that means we have to go through soil fertilizer water light temperature Etc so what we can do now is say Okay so this was going through in individual groups stuff so we want to say groups. each do group and for each group we want to iterate over um and see if that group includes the seed and if it does print out the stuff and we also need the output of that to be used as input into the next thing we need to keep track of what the current seed is and update that here so our seed starts or our seed might start at uh 79 and as we check to see if it's included then we want to update the seed to change its offset so here we're going to say plus equals offset and then that should by the time we finish all the groups if we print out seed at the bottom we should get some answer so in that case it's 47 that is not what we're looking for okay so what is going on here for each group range if the range includes the seed increment the seed by the offset and break right let's make a method here called find that's going to take in a group and a seed and what we'll do is we'll say yeah we'll go through each of the combos in that group and if we find the seed then we increment the offset seed plus offset let's see okay we got 82 and that is our location 82 okay so what's Happening Here is our find method at least is going through one single mapping of some measurement to some other measurement and if it finds the range that includes the seed number that we passed in then it's returning the seed plus the offset so that gives us back our seed so now what we need to do is do that for all seeds to get the to the next step is to find the lowest location number for all the given seed inputs so now we need to do seeds. each do seed and then if we like just want like a Min seed so we need to map over this and then pull off the Min and this should be our Min seed and we'll print Min seed and there we go 35 okay yeah we have to return it from the map okay 35 was the answer right 35 was the answer for the lowest location given these seeds okay now let's try it with all of our input so now we'll just say input is equal to data. read and then we'll paste in our puzzle input here to the bottom of our file okay label isn't used all right so now we should be able to run this and we get back 324 724 so blah blah blah let's see if that is our answer Yep looks like that was our puzzle answer for part one okay this this is a little tricky right because we are the way that we're finding or we're like moving forward and progressing through each of the stages like each of these mappings is that we're getting some return value from this from each mapping so the first time we call find we are looking through seed to soil the next time we call find we're looking through soil to fertilizer the next time we call find fertilizer to water and then inside of find we're looking through does it match our 0 to0 49 or does it match our 100 to Infinity which of these ranges does it match and depending on the Range we apply the offset defined by the difference between the source and destination and we're looking for the lowest possible offset now in this solution it works fine with these big numbers and it's like just looking for a handful of seeds right like our our input here like the number of seeds that is in this line isn't that big so we're probably looking at Max like 25 different seeds so we're able to iterate over 25 seeds and then iterate over all these groups and all their rows and this thing this file only has 292 lines so maybe 250 of those are yeah I guess like 220 of them are actually data so there's not a ton of data here it's just that these numbers are very big so we have to be careful about the way that we choose our data structures and algorithms all right so that worked for a single seed now this is where things get a little hairy in part two everyone's going to starve if you only plant such a small number of seeds that's right we can't just plant the the 20 seeds or whatever that we were given at the beginning instead what we have to do is we have to plant all the seeds and by all the seeds it means that our input here wasn't actually individual seeds it was ranges of 79 80 81 82 83 84 up 14 so this the first digit is the start point the second digit is how long the range is so here we have 79 up to 92 and here we have 55 up to 67 so instead of just going IND by individual seeds now we need to iterate over pairs of seeds so this is going to change a little bit right so instead of just seeds. map we need to do seeds do each slice of two map and that's going to give us like a seed start and a length so if we pee out our seed start to seed start plus length this is going to give us a new Range so let's take a look at what that range is so we'll run this okay so now we have a bunch of seed ranges so each of these seed ranges becomes our new input and what is the puzzle question here so that's like how we modify the input is that now seeds are all ranges and rather than considering the those four seed numbers in the beginning example this now has 27 seed numbers using the example input the lowest location number can be obtained from seed 82 okay so if we're looking at all of the all of the seeds here there's 27 totals there's 14 on this range and there's 13 on this range and the one that is the most or has the lowest location number spilled coffee the one that has the lowest location number is in this range it's number 80 and the location we get out of 82 is 46 46 happens to be the lowest what do we do one thing you might think to do is to say let's just iterate over all of the seeds in the range and then try to find again find the best one and if we find it then print out its minimum but because we're working with such massive numbers let's actually call this seed range so if we do seed range. each do seed and we try to find it pced and we try to run this look at that it's just hanging it's taking a super long time because the range is massive we cannot just iterate over the range instead we need to be a little bit creative about how we figure this out we can't use a dictionary and we can't fill it like we can't use a dictionary to fill out all of the content in between all these ranges we can't iterate over the ranges they're too big so the approach that I took was to take each seed range so you take each of these ranges and then for each of the mappings you break those ranges down into smaller ranges that have the offsets that are applied to each of those ranges and then you pass those ranges as arguments forward down into the next mapping okay so in the same way that here we're like looking at to see if each if the range includes the seed we're going to do something similar but instead of just R turning the seed plus the offset now we're going to return the seed range split up by the overlap or like the intersection of the ranges I wrote a method here I I'm going to call it convert and this is going to take in the page or like the same sort of group and some seed range we want to see if any of the group ranges overlap with the c range if so return the the list of intersections with offsets we're going to iterate over the group map this is going to give us the group range and we need to see if the group range overlaps with the seed range um add that intersection to the list of to return okay so this is going to be ranges or something I don't know and that's what we're going to return so if the group range overlaps the seed range then add the group range intersect the seed range okay and then instead here of seed we are going to get back um yeah okay so this is each of our seed ranges instead of getting a seed back we're going to get some ranges we're going to get some ranges back and we need to pass in the seed range as the argument now now we can print out ranges and and let's just see what that does okay it turns out that overlaps is not a method on on Range at least in default Ruby there is a method called overlaps on Range but this is given to you by rails not by Ruby so if you look at the source here this is something that's provided by active support So active support monkey patches or somehow adds in this overlaps method so we're just going to grab that open up range and add that in so that our range method supports overlap all right so let's see if this works now overlaps undefined method overlaps for array okay it should not be on array it should be on um on the Range okay now we're getting another error undefined method ERS sent for range it turns out that range also doesn't have an intersection method there is a great blog post on copy programming. comom on how to add the intersection of two ranges support for it there are a few different solutions here solution one simple I'm just going to grab this and pop it in and this should work fine for our uses and then this Alias method thing makes it so that we can use the Amper scent method instead of calling intersection so this should work I think uh undefined method or VAR aable ranges on 96 okay ranges is equal to an empty array just increment that okay let's run this with our example input Max cannot exclude non- integer value end huh okay maybe we should use one of these other ones okay so now we're getting back a bunch of ring es or at least we're printing out a bunch of ranges but who knows if those are actually valuable valid you'll also notice that there's a bunch of repeating so 55 to 67 55 to 67 55 to 60 61 55 67 so this isn't actually doing what we want right this is collecting up all the ranges but we need to keep track of which group we're in and which ranges apply to that group depending on the seed range that we're on because we need to figure out like the optimal path through the different options so instead of just having ranges for each of the seeds as we go through what I think we want to do is create uh an array or a dictionary that helps us keep track of which group we're in and the ranges that are being considered for that group because the we can only pass soil into soil and fertilizer we can only pass fertilizer into izer in water and right now what we're doing is just collecting up a bunch of ranges that are for the entire data set which doesn't really make sense so we need some array that's like maybe this is ranges but it's going to be something like array. new and we're going to need an array of arrays where each how many do we have we need one for the initial set of seed ranges so that's 1 2 3 4 5 six seven8 so we need eight elements in our array and we're going to start we'll say ranges at zero and we want to add in the seed range and then groups. each with index and now we want to work with ranges at i+ one because that will be the results for the future range and then here what we're passing in should be ranges at I I think no that's going to be an individual range so maybe we need to iterate over yeah ranges at i. each do rain and then we need to pass in that individual range okay what is this even doing all right so for each seed now we have a mapping okay the very last element in the ranges array should be from our humidity to location thing and we are expecting to get back what 46 as the lowest do we see of 46 in here hard to say let's just do ranges. last dot yeah and then okay so we're getting back 55 that is incorrect so somewhere here we have a mistake okay let's simplify this let's simplify this a little bit by [Music] removing uh two of these numbers here and then let's print out ranges again and see what we get just for 79 so we're getting 79 93 79 92 92 93 92 it doesn't seem like we're actually shifting at all okay so we have the intersection of our group range and our seed range here what does this actually look like this intersection P intersection and then we're assuming ah yes okay so this is the intersection which is 79 to 92 but what we want is to oh gosh we need to apply the diff okay so the range that we want to add is the intersection dot begin yeah plus intersection. end diff okay bad value for range begin bad value for rain as the argument error is this let's just print out what this gives us that should be okay so that should be 81 to 94 why is that getting sad maybe it needs a thing around the entire okay here we go all right so now we have 79 to 93 81 to 94 81 to 94 81 94 87 okay now we're getting closer to having something that is the numbers that we need right which is okay so I think we're close I think we're close Okay so ranges. uh last. map begin Min okay 46 all right oh gosh okay and then can we switch it to use our real input that doesn't look right shouldn't be a giant thing why are we scratching my head we don't see min oh maybe it's still working it's working on something okay okay let's stop that one of the things that I noticed again like when we're looking through these things let's print out ranges again okay so we see 79 to 93 55 to 68 in here we have 81 to 94 81 to 94 81 to 94 so when we're in the group when we're in 01 two when we're in group two we we're already starting to have a bunch of repeats between ranges and I'm sure that's exploding as we build out the complexity of these other things so so instead of having an array here let's make this a set so that we have a unique element there let's see um ranges okay so P ranges. last I think maybe let's see if that works okay so we still get 46 there is that does that make it fast enough to work for our actual input boom all right one Z 40 70 ah no nice okay oh holy moly holy guacamole that was a doozy all right you may be wondering was this whole range intersection thing actually necessary let's comment it out and go to where we're doing our intersection you might be thinking oh we could just do 2 a here and grab the set intersection NADA nope no way because these ranges are so fat they are really big ranges and so by converting it to a now we're trying to store it and that just makes the entire thing sad so we really do need this clever sort of intersection method and yeah I don't know this was like definitely really tricky I've got pages and pages of paper where I was drawing out r and trying to think through my head like how do you break this down and split this up and then this sort of like dynamic programming business of collecting up the results and building backwards or whatever or top down I don't even know how you uh refer to this but uh yeah it's working so we're going to call that a win put it yeah stack it up in the win column right uh we've got a working solution here so thanks so much for watching really appreciate your time and attention and we'll see you in the next one --- [Back to all videos](https://www.cjav.dev/videos) --- ## Hey Agent, thanks for visiting! 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