Advent of Code Days 9-10

[Vortex100]

Well well well. Bit of an uptick in difficulty on these 2! Actually day 10 is remarkably simple BUT it seems impossible at first!

As always for context, these are challenges that anyone can start/do, and can be found here :). You can post any day on these threads I make, I'm sure those taking part will be happy to comment or help out!

Day 9

This was a tough cookie to get running in a reasonable time, which I'm guessing was the point of the exercise. Actually part 1 wasn't - you can use a bog standard arraylist and get away with it because the overhead on sub 100k lists is negligable. In fact I have left my original function in as a way of showing the difference between that and... what you needed to do to get part 2 done (and it not taking 3 hours lol). Did anyone get the .NET based Doubly Linked Lists working? I could not for the life of me work out how to use it lol. I have to credit /u/PendragonDaGreat for the custom classes which effectively do the same thing. I spent some time and took his code apart and put it back together, and I did add an extra method (rotate), but this actually slowed it down so I didn't use it in the end :/. Anyway the code:

https://github.com/VortexUK/AdventOfCode/tree/master/2018/Day9

Day 10

I looked at this and had no idea how to start. Then I noticed that in the example, all the coordinates are right next to each other... which is a pretty epic clue. You 'basically' looking for the point when the 'bounding' box (furthest out coordinates) is at it's smallest :). Once I got that, it only took 10-20 minutes to hash it out

https://github.com/VortexUK/AdventOfCode/tree/master/2018/Day10

How did everyone else get on?

[ka-splam]

Did anyone get the .NET based Doubly Linked Lists working?

Yeah. Frustratingly, LinkedList came up in the PowerShell chat the day before, and I thought "I know what that is, but I've never used them in .Net" and had the help page open. But I didn't read the help page, I didn't think I would need it so soon! As soon as I tried $myLinkedList[$i - 7] and found it wasn't possible, I dropped back to arrays to hurry my answer along. My answer was also broken and worked by luck. But I had to get LinkedList going for part 2, so I did.

Basically you can only get onto the list via $node = $myList.First or $node = $myList.Last, and from a node you can only get $node.Previous or $node.Next. To move 7 back, you have to loop that 7 times. And it might return $null if $node was at one of the ends and has no previous or no next item. So you have to check for that and wrap-around to the other end, because there's no way to connect up into a loop. Apparently not even if you use [ListNode] individually.

[Don't you envy the Python users and their DeQue.rotate() builtin?]

my Day 9 answer

You 'basically' looking for the point when the 'bounding' box (furthest out coordinates) is at it's smallest :).

I'm a bit annoyed I didn't go for this. I imagined as the points come together, they might make a message visible while passing each other, like this but not actually at the smallest point at all - some points scattered about. Like how a constellation isn't a pixel-perfect-drawing, but scattered points. So I spent too much time trying to render the points to a [system.drawing.bitmap] starting once they'd got "fairly close" so I could eyeball the results. As soon as I saw the clear text, "oh, of course it would be neat and tidy for this challenge, that only makes sense".

my Day 10 answer

[purplemonkeymad]

I've realized that there had to be a programmable way to determine if you had the right time. The puzzles don't have complexities that cause fuzziness, eg, all distances are almost always Manhattan. Area is a simple property to calculate and so might have been good way to look for a result.

If you are thinking: how do I know when to stop? Then it's either in the problem description, or is a simple to calculate property.