this post was submitted on 21 Mar 2025
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Advent Of Code

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An unofficial home for the advent of code community on programming.dev!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2024

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why should we sort 2024-day1 ? (self.advent_of_code)
submitted 1 week ago* (last edited 1 week ago) by somegeek to c/advent_of_code
 

Hi guys.

I just did day1 of 2024 (I know, I'm late) this might be a dumb question but I reallydont understand why we should sort the two lists before substracting? I created some test cases with 10-20 items and calculated them manually, if you don't sort the list and just add all list1 items and substract from the sum of list2, you get the same answer. But it doesn't work with the large input file.

Let's say list1 has elements (a,b,c,d) and list2 has (e,f,g,h).

(a-e)+(b-f)+(c-g)+(d-h) = a-e+b-f+c-g+d-h = (a+b+c+d)-(e+f+g+h)

So the sorting shouldn't matter. Right? But it does. Am I too bad at basic math?

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[–] [email protected] 2 points 1 week ago

There's a way to make two length-two lists from 1, 2, 3, 4 that will give you a counter-example.