2015 day 13

AOC.Test/Test2015.cs

@@ -18,6 +18,7 @@ public class Test2015
     [DataRow(typeof(Day10), "492982", "6989950")]
     [DataRow(typeof(Day11), "hepxxyzz", "heqaabcc")]
     [DataRow(typeof(Day12), "111754", "65402")]
+    [DataRow(typeof(Day13), "733", "725")]
     public void CheckAllDays(Type dayType, string part1, string part2)
     {
         Common.CheckDay(dayType, part1, part2);
@@ -34,6 +35,7 @@ public class Test2015
     [DataRow(typeof(Day08), "12", "19")]
     [DataRow(typeof(Day09), "605", "982")]
     [DataRow(typeof(Day10), "237746", "3369156")]
+    [DataRow(typeof(Day13), "330", "286")]
     public void CheckTestInputs(Type dayType, string part1, string part2)
     {
         Common.CheckDay(dayType, part1, part2, true);

AOC2015/Day13.cs

@@ -1,3 +1,5 @@
+//using MoreLinq.Extensions;
+
 namespace AOC2015;
 
 /// <summary>
@@ -7,9 +9,85 @@ public sealed class Day13 : Day
 {
     public Day13() : base(2015, 13, "Knights of the Dinner Table")
     {
+        foreach (var line in Input)
+            AddToHappinessMap(line);
     }
 
-    public override object Part1() => "";
+    public override object Part1()
+    {
+        return ComputeHappiness();
+    }
 
-    public override object Part2() => "";
-}
+    public override object Part2()
+    {
+        //  Add myself
+        foreach (var person in allPeople)
+        {
+            happinessMap[("me", person)] = 0;
+            happinessMap[(person, "me")] = 0;
+        }
+        
+        allPeople.Add("me");
+
+        return ComputeHappiness();
+    }
+
+    private Dictionary<(string person1, string person2), int> happinessMap = new();
+    private List<string> allPeople = new();
+
+    private void AddToHappinessMap(string thisString)
+    {
+        var tokens = thisString.Split(' ');
+        var firstPerson = tokens.First();
+        var lastPerson = tokens.Last().TrimEnd('.');
+        var amount = int.Parse(tokens[3]);
+
+        if (tokens.Contains("lose"))
+            amount *= -1;
+
+        happinessMap[(firstPerson, lastPerson)] = amount;
+
+        if (!allPeople.Contains(firstPerson))
+            allPeople.Add(firstPerson);
+        if (!allPeople.Contains(lastPerson))
+            allPeople.Add(lastPerson);
+    }
+
+
+    public static List<List<string>> BuildPermutations(List<string> items)
+    {
+        if (items.Count > 1)
+        {
+            return items.SelectMany(item => BuildPermutations(items.Where(i => !i.Equals(item)).ToList()),
+                (item, permutation) => new[] { item }.Concat(permutation).ToList()).ToList();
+        }
+
+        return new() { items };
+    }
+
+    public long ComputeHappiness()
+    {
+        var possibilities = BuildPermutations(allPeople);
+
+        var maxHappiness = long.MinValue;
+        foreach (var possibility in possibilities)
+        {
+            long thisPossibilityHappiness = 0;
+
+            for (var i = 0; i < possibility.Count; i++)
+            {
+                //  get the people on either side.
+                var firstPerson = possibility[i];
+                var leftPerson = i == 0 ? possibility[^1] : possibility[i - 1];
+                var rightPerson = i == possibility.Count - 1 ? possibility[0] : possibility[i + 1];
+
+                thisPossibilityHappiness += happinessMap[(firstPerson, leftPerson)];
+                thisPossibilityHappiness += happinessMap[(firstPerson, rightPerson)];
+            }
+
+            maxHappiness = Math.Max(maxHappiness, thisPossibilityHappiness);
+        }
+
+        return maxHappiness;
+    }
+}

AOC2015/input2015/test13.in

@@ -0,0 +1,12 @@
+Alice would gain 54 happiness units by sitting next to Bob.
+Alice would lose 79 happiness units by sitting next to Carol.
+Alice would lose 2 happiness units by sitting next to David.
+Bob would gain 83 happiness units by sitting next to Alice.
+Bob would lose 7 happiness units by sitting next to Carol.
+Bob would lose 63 happiness units by sitting next to David.
+Carol would lose 62 happiness units by sitting next to Alice.
+Carol would gain 60 happiness units by sitting next to Bob.
+Carol would gain 55 happiness units by sitting next to David.
+David would gain 46 happiness units by sitting next to Alice.
+David would lose 7 happiness units by sitting next to Bob.
+David would gain 41 happiness units by sitting next to Carol.