Day 8

Took me a little while to understand the problem, but once I did, ivec2 came in clutch once again.

Would have had part 2 sooner if not for the "also all antennas are now antinodes" thing which I just missed. You win again, reading comprehension.

src/08.cs

@@ -0,0 +1,93 @@
+using aoc2024.Util;
+
+namespace aoc2024;
+
+internal class Day08 : Day
+{
+    private readonly Dictionary<char, List<ivec2>> antennas = [];
+    private ivec2 dimensions = ivec2.ZERO;
+
+    internal override void Parse()
+    {
+        var lines = Util.Parsing.ReadAllLines($"{GetDay()}").ToList();
+        dimensions = new ivec2(lines[0].Length, lines.Count);
+        for (int i = 0; i < lines.Count; i++)
+        {
+            var line = lines[i];
+            for (int j = 0; j < line.Length; j++)
+            {
+                if (line[j] == '.' || line[j] == '#')
+                {
+                    continue;
+                }
+
+                var loc = new ivec2(j, i);
+                if (!antennas.TryAdd(line[j], [loc]))
+                {
+                    antennas[line[j]].Add(loc);
+                }
+            }
+        }
+    }
+
+    internal override string Part1()
+    {
+        HashSet<ivec2> antinodes = [];
+        foreach (var (_, locs) in antennas)
+        {
+            foreach (var loc in locs)
+            {
+                var others = locs.Except([loc]);
+                foreach (var other in others)
+                {
+                    var between = loc - other;
+                    var a1 = loc + between;
+                    var a2 = other - between;
+                    if (a1.IsWithinRange(0, 0, dimensions.x - 1, dimensions.y - 1))
+                    {
+                        antinodes.Add(loc + between);
+                    }
+
+                    if (a2.IsWithinRange(0, 0, dimensions.x - 1, dimensions.y - 1))
+                    {
+                        antinodes.Add(other - between);
+                    }
+                }
+            }
+        }
+
+        return $"# antinodes: <+white>{antinodes.Count}";
+    }
+
+    internal override string Part2()
+    {
+        HashSet<ivec2> antinodes = [];
+        foreach (var (_, locs) in antennas)
+        {
+            antinodes.UnionWith(locs);
+            foreach (var loc in locs)
+            {
+                var others = locs.Except([loc]);
+                foreach (var other in others)
+                {
+                    var between = loc - other;
+                    var a1 = loc + between;
+                    var a2 = other - between;
+                    while (a1.IsWithinRange(0, 0, dimensions.x - 1, dimensions.y - 1))
+                    {
+                        antinodes.Add(a1);
+                        a1 += between;
+                    }
+
+                    while (a2.IsWithinRange(0, 0, dimensions.x - 1, dimensions.y - 1))
+                    {
+                        antinodes.Add(a2);
+                        a2 -= between;
+                    }
+                }
+            }
+        }
+
+        return $"# antinodes including harmonics: <+white>{antinodes.Count}";
+    }
+}

src/Util/Vec2.cs

@@ -74,7 +74,7 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
         }
     }
 
-    public IEnumerable<ivec2> GetBoundedOrthogonalNeighbors(int minX, int minY, int maxX, int maxY)
+    public IEnumerable<ivec2> GetBoundedOrthogonalNeighbors(long minX, long minY, long maxX, long maxY)
     {
         foreach (var dir in FOURWAY)
         {
@@ -96,7 +96,7 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
         }
     }
 
-    public IEnumerable<ivec2> GetBoundedNeighbors(int minX, int minY, int maxX, int maxY)
+    public IEnumerable<ivec2> GetBoundedNeighbors(long minX, long minY, long maxX, long maxY)
     {
         foreach (var dir in EIGHTWAY)
         {
@@ -118,7 +118,7 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
         }
     }
 
-    public IEnumerable<ivec2> GetBoundedDiagonalNeighbors(int minX, int minY, int maxX, int maxY)
+    public IEnumerable<ivec2> GetBoundedDiagonalNeighbors(long minX, long minY, long maxX, long maxY)
     {
         foreach (var dir in DIAGONALS)
         {
@@ -149,17 +149,11 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
     public static bool operator >(ivec2 a, ivec2 b) => (a.x > b.x) && (a.y > b.y);
     public static bool operator >=(ivec2 a, ivec2 b) => (a.x >= b.x) && (a.y >= b.y);
 
-    public bool IsWithinRange(int minX, int minY, int maxX, int maxY) => x >= minX && y >= minY && x <= maxX && y <= maxY;
+    public bool IsWithinRange(long minX, long minY, long maxX, long maxY) => x >= minX && y >= minY && x <= maxX && y <= maxY;
 
-    public bool Equals(ivec2 other)
-    {
-        return x == other.x && y == other.y;
-    }
+    public bool Equals(ivec2 other) => x == other.x && y == other.y;
 
-    public override bool Equals(object? obj)
-    {
-        return obj is ivec2 other && Equals(other);
-    }
+    public override bool Equals(object? obj) => obj is ivec2 other && Equals(other);
 
     public int CompareTo(ivec2 other)
     {
@@ -178,7 +172,11 @@ public readonly struct ivec2 : IEquatable<ivec2>, IComparable<ivec2>, IComparabl
 
     public int CompareTo(object? obj)
     {
-        if (ReferenceEquals(null, obj)) return 1;
+        if (obj is null)
+        {
+            return 1;
+        }
+
         return obj is ivec2 other ? CompareTo(other) : throw new ArgumentException($"Object must be of type {nameof(ivec2)}");
     }
 

src/main.cs

@@ -115,12 +115,11 @@ else
 
 foreach (var desiredDay in desiredDays)
 {
-    Day? day = getDayInstanceFromArg(desiredDay);
+    using Day? day = getDayInstanceFromArg(desiredDay);
     if (day == null)
     {
         Logger.LogLine($"Unknown day <cyan>{desiredDay}<r>");
     }
 
     day?.Go(runPart1 ?? true, runPart2 ?? true);
-    day?.Dispose();
 }