feat: AoC 2025 Day 9 Part 1

src/AdventOfCode.Puzzles/2025/09/Part1/Solution.cs

@@ -0,0 +1,35 @@
+namespace AdventOfCode.Puzzles._2025._09.Part1;
+
+public class Solution : IPuzzleSolution
+{
+    public async Task<string> SolveAsync(StreamReader inputReader)
+    {
+        var lines = await inputReader.ReadAllLinesAsync();
+
+        var points = new List<Point>();
+
+        foreach (var line in lines)
+        {
+            var parts = line.Split(',');
+            var x = int.Parse(parts[0]);
+            var y = int.Parse(parts[1]);
+            points.Add(new Point(x, y));
+        }
+
+        var maxArea = 0L;
+        foreach (var point1 in points)
+        {
+            foreach (var point2 in points)
+            {
+                // Area
+                var area = (long)(Math.Abs(point1.X - point2.X) + 1) * (Math.Abs(point1.Y - point2.Y) + 1);
+                if (maxArea < area)
+                {
+                    maxArea = area;
+                }
+            }
+        }
+
+        return maxArea.ToString();
+    }
+}

src/AdventOfCode.Puzzles/2025/09/TestData.txt

@@ -0,0 +1,8 @@
+7,1
+11,1
+11,7
+9,7
+9,5
+2,5
+2,3
+7,3