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why should we sort 2024-day1 ?
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this post was submitted on 21 Mar 2025
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Advent Of Code
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It doesn't ask you to subtract the numbers, but to calculate the distance (i.e. the absolute value of the subtraction). So depending on which numbers are paired up, the sign of the pair can be different.
True, that is what I did when substracting the sorted lists. I calculated their absolutes.
But I still don't understand why the unsorted method doesn't work. Can you give an example of two lists which this method doesn't work with? Because whatever example I calculated, it was correct.
There's a way to make two length-two lists from 1, 2, 3, 4 that will give you a counter-example.
gives 27
But
gives 11
You are right. Although the way I was talking about is |(2+10)-(1+20)|= 9 Seems like I coincidentally created some example lists that all worked with this method!
And the algebraic reason would be the presence of parenthesis. |(a+b)-(c+d)| != |(a-c)|+|(b-d)|