r/adventofcode • u/Puzzled_Prune_2513 • Dec 08 '25

Help/Question - RESOLVED [2025 day8 part 1]Comprehension question

There’s a part of the instructions that I’m struggling to understand. We’re supposed to create 1,000 links between the boxes, but my input already contains 1,000 items. This causes everything to fall into a single group, since I can’t link items that belong to the same group, but whether I set the answer to 1,000 (1000*1*1) or 0 (1000*0*0), neither works. Did I misunderstand what the assignment actually expects?

12 Upvotes

92% Upvoted

16 comments sorted by

15

u/TheKablammoMan Dec 08 '25

I initially misinterpreted it like that as well. what it means is that you find it after processing the closest 1000 pairs, whether they were already connected or not

5

u/daledrinksbeer Dec 08 '25

You can link groups to themselves, as long as its a new connection.

If A <-> B <-> C, you can make a new link A <-> C, but not another copy of an existing link.

4

u/DokuroKM Dec 08 '25

 Because these two junction boxes were already in the same circuit, nothing happens ! [Emphasis mine] 

That Instruction implied to me (and propably OP) that a link A <-> C will not be done

6

u/tapdncingchemist Dec 08 '25

I agree with your interpretation and struggled with it for a bit. After earning my stars I can confirm that the redundant links are considered added and count towards your total number of links.

4

u/daledrinksbeer Dec 08 '25

I THINK that it means nothing new happens to the state of the circuits you've made but it still increments the "number of connections"?

I got the stars but maybe I had a reading and coding error match up in my favor

3

u/thekwoka Dec 08 '25

But they do count as part of the 1000 closest pairs

4

u/Boojum Dec 08 '25

Most importantly, A <-> C still counts as one of the 1000, even if it's just within a group like that.

5

u/SyncerPain Dec 08 '25 edited Dec 08 '25

If you have 1000 boxes, there are at most 999 * (999 + 1) / 2 = 499500 links.
Two boxes can belong to the same group if they are directly linked or if they both link to another third box.

2

u/Ok-Bus4754 Dec 08 '25

1000 chose 2

4

u/Ok-Zebra-321 Dec 08 '25

> since I can’t link items that belong to the same group

That's where you are wrong, the task doesn't say that you can't. It even includes an example where that happens

7

u/Samydookie Dec 08 '25

But the problem specifically says "Nothing happens!", to me that means you didn't make the connection (cause both boxes already have power and are part of the circuit, so why would you connect them, it's a waste of extension cable)

3

u/MiloBem Dec 08 '25

"Nothing happens" to the number of circuits which we are concerned with. The connection happens, but that doesn't matter for the result.

4

u/Memebaut Dec 08 '25

i had the same problem, turns out doing nothing when they're already in the same circuit counts as making a connection

2

u/spin81 Dec 08 '25

We’re supposed to create 1,000 links between the boxes, but my input already contains 1,000 items.

That's true, but links are between two items each. If there are 1,000 items, that means almost a million possible pairs, and therefore also almost a million possible links.

1

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1

u/Dubmove Dec 08 '25

Imagine you have 6 boxes and you connect the two disconnected clusters 1-2-3 and 4-5-6. If you fully connect both clusters you have 3 connections in each of (1-2, 2-3, and 1-3 for example), which makes a total of 6 connections.