Add Day12 implementation with puzzle-solving logic and tests

AoC_2025.Tests/Day12Test.cs

@@ -0,0 +1,47 @@
+using AdvenOfCode.Contracts;
+
+namespace AoC_2025.Tests;
+
+public class Day12Test
+{
+    private IPuzzleSolver<long> _sut;
+    private static readonly string rootPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
+    private readonly string TestInputPath = @$"{rootPath}\AoC-PuzzleInputs\2025\Test\day12.txt";
+    private readonly string ProdInputPath = @$"{rootPath}\AoC-PuzzleInputs\2025\Prod\day12.txt";
+    
+    public Day12Test()
+    {
+        _sut = new Day12();
+    }
+    [Fact]
+    public void Part01_Test_equals_2()
+    {
+        var actual = _sut.SolvePart1(TestInputPath);
+        
+        Assert.Equal(2, actual);
+    }
+    
+    [Fact]
+    public void Part01_Prod_equals_460()
+    {
+        var actual = _sut.SolvePart1(ProdInputPath);
+        
+        Assert.Equal(460, actual);
+    }
+    
+    [Fact]
+    public void Part02_Test2_equals_0()
+    {
+        var actual = _sut.SolvePart2(TestInputPath);
+        
+        Assert.Equal(0, actual);
+    }
+    
+    [Fact]
+    public void Part02_Prod_equals_0()
+    {
+        var actual = _sut.SolvePart2(ProdInputPath);
+        
+        Assert.Equal(0, actual);
+    }
+}

AoC_2025/Day12.cs

@@ -0,0 +1,51 @@
+using System;
+using System.Collections.Generic;
+using System.Data;
+using System.Data.Common;
+using System.IO;
+using System.Linq;
+using AdvenOfCode.Contracts;
+
+namespace AoC_2025;
+
+public class Day12 : IPuzzleSolver<long>
+{
+    private (int[] presentSizes, (int area, int[] presentCounts)[] regions) ParsePuzzleInput(string path)
+    {
+        var puzzleInput = File.ReadAllText(path)
+            .Split($"{Environment.NewLine}{Environment.NewLine}", StringSplitOptions.TrimEntries)
+            .ToList();
+        var presentSizes = puzzleInput[..^1]
+            .Where(s => !string.IsNullOrWhiteSpace(s))
+            .Select(s => s.Count(c => c == '#'))
+            .ToArray();
+        var regions = puzzleInput[^1]
+            .Split(Environment.NewLine, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+            .Select(s => s.Split(':', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
+            .Select(s => 
+                (s[0].Split('x').Select(int.Parse).Aggregate((x, y) => x * y),
+                 s[1].Split(' ').Select(int.Parse).ToArray()))
+            .ToArray();
+        return (presentSizes, regions);
+    }
+
+    public long SolvePart1(string pathToPuzzleInput)
+    {
+        var (presentSizes, regions) = ParsePuzzleInput(pathToPuzzleInput);
+        var everythingFits =
+            regions.Count(region => region.area >= GetMinTotalPresentArea(region.presentCounts, presentSizes));
+        return everythingFits;
+    }
+
+    private static int GetMinTotalPresentArea(int[] presentCounts, int[] presentSizes)
+    {
+        return presentCounts
+            .Select((presentCount, index) => presentCount * presentSizes[index])
+            .Sum();
+    }
+
+    public long SolvePart2(string pathToPuzzleInput)
+    {
+        return 0;
+    }
+}