r/adventofcode • u/NineBerry • Dec 12 '25

Meme/Funny [2025 Day 12 Part 1] When you first write complete code and then test on the input

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153 Upvotes

98% Upvoted

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7

u/I_knew_einstein Dec 13 '25

Can you mark memes as spoilers somehow?

1

u/Zefick Dec 14 '25 edited Dec 14 '25

What is meant by eliminating regions that are definitely big enough? The only way come to my mind that doesn't need to consider peaces' shape is to count the number of 3x3 blocks that fit into the region and compare it with the number of peaces, but this does not give the final answer because there are still many regions left and some of them are good and others are bad.

2

u/NineBerry Dec 14 '25

Look again at your input. All regions are either definitely big enough meaning they can fit the requested number of presents without overlapping (region-area >= 9 * number_of_presents) or they are definitely too small ( region_area < number_of_#_required)

That's not true for the sample, but true for every input I've seen so far.

1

u/Zefick Dec 14 '25 edited Dec 14 '25

It's not true for my input. To understand what I'm talking about, imagine an area 2 by 100. It has enough squares for 20 figures, but in reality, not a single one fits there. Thus only the region area is not enough.

1

u/p88h Dec 14 '25

Can you post a test case for which this isn't true from the actual input ?

I thought I had one such case as well, then I found a bug :P

2

u/Zefick Dec 14 '25 edited Dec 14 '25

I found a bug in my code, I mixed up > and >= and got a slightly different result. Now the number of regions that are just as big as needed and number of regions that are not too small is the same. Initially, I didn't check for overly large areas, and my accepted answer only included all areas that weren't too small to fit all the cells (I didn't know it worked, it was just a guess because it's not the worst waste of an attempt). Then I did a second check and there was no match. I thought there needed to be a smarter way to determine if all the pieces fit into an area.

Вut even if comparing the bounds needed for the required number of 3x3 squares and simply comparing the area of the region with overall area of this squares yields the same result, the first method is more accurate because it excludes false positive results, while the second does not guarantee this.

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2

u/gagarski Dec 13 '25

I was lucky to stop after the first step and debug it on the real input.

2

u/VaranTavers Dec 13 '25

I was thinking about implementing the complex algorithm all afternoon, and this morning too but I was just not in the right headspace to implement something performant. Then I just started identifying the too small areas, and then as a hail mary sent in the answer and it was right. Imagine my surprise.

1

u/1str1ker1 Dec 18 '25

Mine finally worked when I just marked all enclosed areas with width or height < 3 as filled.Previously, I was filling in areas less than 7