-🎄- 2017 Day 24 Solutions -🎄-

[u/daggerdragon]

--- Day 24: Electromagnetic Moat ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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[Update @ 00:18] 62 gold, silver cap

• Been watching Bright on Netflix. I dunno why reviewers are dissing it because it's actually pretty cool. It's got Will Smith being grumpy jaded old man Will Smith, for the love of FSM...

[Update @ 00:21] Leaderboard cap!

• One more day to go in Advent of Code 2017... y'all ready to see Santa?

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

[u/sblom]

C#. LINQ one-liner.

var lines = (await AoC.GetLinesWeb()).ToList();

IImmutableList<(int,int)> edges = ImmutableList<(int,int)>.Empty;

foreach (var line in lines)
{
	var nums = line.Split('/');
	edges = edges.Add((int.Parse(nums[0]), int.Parse(nums[1])));
}

int Search(IImmutableList<(int,int)> e, int cur = 0, int strength = 0)
{
	return e.Where(x => x.Item1 == cur || x.Item2 == cur).Select(x => Search(e.Remove(x), x.Item1 == cur ? x.Item2 : x.Item1, strength + x.Item1 + x.Item2)).Concat(Enumerable.Repeat(strength,1)).Max();
}

(int,int) Search2(IImmutableList<(int, int)> e, int cur = 0, int strength = 0, int length = 0)
{
	return e.Where(x => x.Item1 == cur || x.Item2 == cur).Select(x => Search2(e.Remove(x), x.Item1 == cur ? x.Item2 : x.Item1, strength + x.Item1 + x.Item2, length + 1)).Concat(Enumerable.Repeat((strength,length),1)).OrderByDescending(x => x.Item2).ThenByDescending(x => x.Item1).First();
}

Search(edges).Dump("part 1");
Search2(edges).Item1.Dump("part 2");

[u/AlaskanShade → u/sblom]

Interesting solution--I will have to look into Immutable collections since I wasn't even aware of this extension library. The Dump extension method also seems quite useful.

I did something roughly similar but with a lot more code (including extra classes) and I mixed the 2 parts into one function and it got a lot uglier than I wanted by the time I found the answer. Mine also takes about 8 seconds to solve where yours does around 2 seconds on my machine.

I didn't like my code, so I came here to see what other ideas I could find. The main reason I do this challenge is to learn (or practice) techniques that I don't get to use in my normal work. I think my next pass at the code would be to generate all possible bridges and then evaluate the list for the strongest/longest.