Add day 8

Days/Day8.cs

@@ -0,0 +1,169 @@
+using System.Collections.Frozen;
+using System.Numerics;
+using Spectre.Console;
+
+namespace AdventOfCode.Days;
+
+public class Day8 : Day
+{
+    public override int Number => 8;
+    public override string Name => "Resonant Collinearity";
+
+    private const int GridSize = 50;
+
+    public override void RunPart1(bool display = true)
+    {
+        HashSet<Point> antinodePositions = [];
+
+        var frequencyAntennas = ParseAntennas();
+
+        // Find antinodes for each frequency
+        foreach (var (_, antennas) in frequencyAntennas)
+        {
+            // Take antennas by pair to find antinodes
+            foreach (var firstAntenna in antennas)
+            {
+                foreach (var secondAntenna in antennas.Where(a => a != firstAntenna))
+                {
+                    var firstAntinode = firstAntenna + (firstAntenna - secondAntenna);
+                    var secondAntinode = secondAntenna + (secondAntenna - firstAntenna);
+
+                    if (firstAntinode is { X: >= 0 and < GridSize, Y: >= 0 and < GridSize })
+                    {
+                        antinodePositions.Add(firstAntinode);
+                    }
+
+                    if (secondAntinode is { X: >= 0 and < GridSize, Y: >= 0 and < GridSize })
+                    {
+                        antinodePositions.Add(secondAntinode);
+                    }
+                }
+            }
+        }
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Unique antinode positions count: [yellow]{antinodePositions.Count}[/][/]");
+        }
+    }
+
+    public override void RunPart2(bool display = true)
+    {
+        HashSet<Point> antinodePositions = [];
+
+        var frequencyAntennas = ParseAntennas();
+
+        // Find antinodes for each frequency
+        foreach (var (_, antennas) in frequencyAntennas)
+        {
+            // Take antennas by pair to find antinodes
+            foreach (var firstAntenna in antennas)
+            {
+                foreach (var secondAntenna in antennas.Where(a => a != firstAntenna))
+                {
+                    // Always add antinodes on antennas if a pair is formed
+                    antinodePositions.Add(firstAntenna);
+                    antinodePositions.Add(secondAntenna);
+
+                    // Compute potential antinode positions
+                    var firstAntinodeOffset = firstAntenna - secondAntenna;
+                    var secondAntinodeOffset = secondAntenna - firstAntenna;
+
+                    for (var i = 1; ; i++)
+                    {
+                        var firstAntinode = firstAntenna + (i * firstAntinodeOffset);
+
+                        if (firstAntinode is { X: >= 0 and < GridSize, Y: >= 0 and < GridSize })
+                        {
+                            antinodePositions.Add(firstAntinode);
+                        }
+                        else
+                        {
+                            break;
+                        }
+                    }
+
+                    for (var i = 1; ; i++)
+                    {
+                        var secondAntinode = secondAntenna + (i * secondAntinodeOffset);
+
+                        if (secondAntinode is { X: >= 0 and < GridSize, Y: >= 0 and < GridSize })
+                        {
+                            antinodePositions.Add(secondAntinode);
+                        }
+                        else
+                        {
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Unique antinode positions count: [yellow]{antinodePositions.Count}[/][/]");
+        }
+    }
+
+    private FrozenDictionary<char, List<Point>> ParseAntennas()
+    {
+        var antennas = new Dictionary<char, List<Point>>();
+
+        var y = 0;
+        foreach (var line in Input.AsSpan().EnumerateLines())
+        {
+            var x = 0;
+
+            foreach (var frequency in line)
+            {
+                if (frequency is '.')
+                {
+                    x++;
+
+                    continue;
+                }
+
+                if (!antennas.TryGetValue(frequency, out var list))
+                {
+                    list = [];
+                    antennas[frequency] = list;
+                }
+
+                list.Add(new Point(x, y));
+
+                x++;
+            }
+
+            y++;
+        }
+
+        return antennas.ToFrozenDictionary();
+    }
+
+    private readonly record struct Point(int X, int Y)
+        : IAdditionOperators<Point, Point, Point>,
+            ISubtractionOperators<Point, Point, Point>,
+            IMultiplyOperators<Point, int, Point>
+    {
+        public static Point operator +(Point left, Point right)
+        {
+            return new Point(left.X + right.X, left.Y + right.Y);
+        }
+
+        public static Point operator -(Point left, Point right)
+        {
+            return new Point(left.X - right.X, left.Y - right.Y);
+        }
+
+        public static Point operator *(Point left, int right)
+        {
+            return new Point(left.X * right, left.Y * right);
+        }
+
+        public static Point operator *(int left, Point right)
+        {
+            return new Point(right.X * left, right.Y * left);
+        }
+    }
+}