86 lines
2.5 KiB
C#
86 lines
2.5 KiB
C#
namespace AOC2015;
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/// <summary>
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/// Day 13: <a href="https://adventofcode.com/2015/day/13"/>
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/// </summary>
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public sealed class Day13() : Day(2015, 13, "Knights of the Dinner Table")
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{
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private readonly Dictionary<(string person1, string person2), int> _happinessMap = [];
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private readonly List<string> _people = [];
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public override void ProcessInput()
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{
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foreach (var line in Input) AddToHappinessMap(line);
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}
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public override object Part1() => ComputeHappiness();
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public override object Part2()
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{
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// Add myself
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foreach (var person in _people)
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{
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_happinessMap[("me", person)] = 0;
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_happinessMap[(person, "me")] = 0;
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}
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_people.Add("me");
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return ComputeHappiness();
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}
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private void AddToHappinessMap(string thisString)
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{
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var tokens = thisString.Split(' ');
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var person1 = tokens.First();
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var person2 = tokens.Last().TrimEnd('.');
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var amount = int.Parse(tokens[3]);
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if (tokens.Contains("lose"))
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amount *= -1;
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_happinessMap[(person1, person2)] = amount;
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if (!_people.Contains(person1))
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_people.Add(person1);
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if (!_people.Contains(person2))
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_people.Add(person2);
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}
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private static List<List<string>> BuildPermutations(List<string> items)
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{
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if (items.Count > 1)
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{
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return items.SelectMany(item => BuildPermutations(items.Where(i => !i.Equals(item)).ToList()),
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(item, permutation) => new[] { item }.Concat(permutation).ToList()).ToList();
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}
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return [items];
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}
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private long ComputeHappiness()
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{
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var possibilities = BuildPermutations(_people);
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var maxHappiness = long.MinValue;
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foreach (var possibility in possibilities)
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{
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long thisPossibilityHappiness = 0;
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for (var i = 0; i < possibility.Count; i++)
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{
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// get the people on either side.
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var firstPerson = possibility[i];
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var leftPerson = i == 0 ? possibility[^1] : possibility[i - 1];
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var rightPerson = i == possibility.Count - 1 ? possibility[0] : possibility[i + 1];
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thisPossibilityHappiness += _happinessMap[(firstPerson, leftPerson)];
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thisPossibilityHappiness += _happinessMap[(firstPerson, rightPerson)];
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}
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maxHappiness = Math.Max(maxHappiness, thisPossibilityHappiness);
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}
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return maxHappiness;
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}
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} |