2024 Day 14

src/2024/14/Program.cs

@@ -1,6 +1,79 @@
 using AdventOfCode.Common;
+using Coor = AdventOfCode.Common.Coor<int>;
 
-var lines = Resources.GetInputFileLines();
+const int height = 103;
+const int width = 101;
 
-Console.WriteLine($"Part 1: {""}");
-Console.WriteLine($"Part 2: {""}");
+var robots = Resources.GetInputFileLines()
+    .Select(line => line.ParseNumbersOut())
+    .Select(n => new Robot(new Coor(n[1], n[0]), new Coor(n[3], n[2]), width, height))
+    .ToArray();
+
+int second = 0;
+int[,] quadrants = null!;
+while (!IsEasterEgg(robots, width, height))
+{
+    ++second;
+    for (int j = 0; j < robots.Length; ++j)
+    {
+        robots[j].Move();
+    }
+
+    if (second == 100)
+    {
+        quadrants = GetQuadrantCounts(robots, width, height);
+    }
+}
+
+Console.WriteLine($"Part 1: {quadrants[1, 0] * quadrants[1, 1] * quadrants[0, 0] * quadrants[0, 1]}");
+Console.WriteLine($"Part 2: {second}");
+
+static bool IsEasterEgg(Robot[] robots, int width, int height)
+{
+    var border = 5;
+    var inTheMiddle = robots.Count(
+        r => r.Position.X >= border && r.Position.X < width - border
+          && r.Position.Y >= border && r.Position.Y < height - border);
+
+    if (inTheMiddle > robots.Length / 10 * 9)
+    {
+        new char[height, width].Print(c => !robots.Any(r => r.Position == c) ? '.' : (char)(robots.Count(r => r.Position == c) + '0'));
+        return true;
+    }
+
+    return false;
+}
+
+static int[,] GetQuadrantCounts(Robot[] robots, int width, int height)
+{
+    int[,] quadrants = new int[2, 2];
+    int xMid = (width + 1) / 2;
+    int yMid = (height + 1) / 2;
+    for (int j = 0; j < robots.Length; ++j)
+    {
+        var (y, x) = robots[j].Position;
+        if (x == xMid - 1 || y == yMid - 1) continue;
+
+        quadrants[x / xMid, y / yMid] += 1;
+    }
+
+    return quadrants;
+}
+
+file class Robot(Coor position, Coor velocity, int width, int height)
+{
+    private readonly Coor<int> _velocity = velocity;
+    private readonly int _width = width;
+    private readonly int _height = height;
+
+    public Coor<int> Position { get; private set; } = position;
+
+    public void Move()
+    {
+        Position += _velocity;
+        if (Position.Y >= _height) Position = Position with { Y = Position.Y - _height };
+        else if (Position.Y < 0) Position = Position with { Y = Position.Y + _height };
+        if (Position.X >= _width) Position = Position with { X = Position.X - _width };
+        else if (Position.X < 0) Position = Position with { X = Position.X + _width };
+    }
+}