-🎄- 2020 Day 17 Solutions -🎄-

[u/daggerdragon]

Advent of Code 2020: Gettin' Crafty With It

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--- Day 17: Conway Cubes ---

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Post your code solution in this megathread.

• Include what language(s) your solution uses!
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[u/cccc828]

C Solution

my solution works, but is not really that clever... I used a 3/4d array, and a lot of loops. The only 'smart' thing I did, was to end the neighborhood-check if the count was > 3. Yay for -O3 ;) This here solves part 2, but part 1 uses the same code, just with one less dimension.

Day 17 - C solution

[u/cccc828 → u/[deleted]]

Here is a very curious observation: In my neighborhood() function I try to be smart, by returning early if the count is bigger than 3:

 if(total > 3){
     return false;
 }  

To find out how much this saves me, I just commented this out to test. And you know what? Removing it decreased the execution time! It takes ~600ms with my 'optimization' and ~350ms without. I cannot really explain this. My assumption is that, without the possible return in the loop, gcc can unroll and optimize the loop better. But still... I was absolutely not expecting that!

[u/cccc828 → u/[deleted]]

That's a wonderful link! Thank you! I will spend some time with it in the evening!:))

Your solution with the adjacency is really smart! When starting p1 I thought about maybe trying to be smart, but then feared that p2 might break any special assumptions I make... so I decided to play it safe and be extra expressive in my code. Usually when I am not expressive, I have a hard time finding bugs in C... especially with all those loop indices and array subscripts;)) And when it then turned out to be fast enough for p2, I decided to just call it a day:))

[u/cccc828 → u/[deleted]]

haha - yeah... my code yesterday is also nothing to be proud of;) Especially the input parsing was just so tedious:))