why should we sort 2024-day1 ?
why should we sort 2024-day1 ?
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?
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.
10 1 2 20gives 27
But
2 1 10 20gives 11