Add Day 9

Day9/Day9.csproj

@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net8.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <None Update="input.txt">
+        <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      </None>
+    </ItemGroup>
+
+</Project>

Day9/Program.cs

@@ -0,0 +1,113 @@
+var diskMap = File.ReadAllText("input.txt");
+var disk = GenerateFileSystem(diskMap); // I could create a class for this, but... meh
+var part1 = DefragBlocks(new List<int>(disk.Item1));
+var part2 = DefragFiles(new List<int>(disk.Item1), new List<(int Id, int Length, int Position)>(disk.Item2), disk.Item3);
+
+Console.WriteLine($"Part1: {part1}\nPart2: {part2}");
+
+long DefragFiles(List<int> fileSystem, List<(int Id, int Length, int Position)> files, List<(int Length, int Position)> free)
+{
+    for (var i = files.Count - 1; i >= 0; i--)
+    {
+        var file = files[i];
+        for (var j = 0; j < free.Count; j++)
+        {
+            var slot = free[j];
+            if (file.Position < slot.Position)
+            {
+                break;
+            }
+
+            if (slot.Length >= file.Length)
+            {
+                for (var k = 0; k < file.Length; k++)
+                {
+                    (fileSystem[slot.Position + k], fileSystem[file.Position + k]) = (fileSystem[file.Position + k], fileSystem[slot.Position + k]);
+                }
+
+                free[j] = (slot.Length - file.Length, slot.Position + file.Length);
+
+                break;
+            }
+        }
+    }
+
+    return CalculateChecksum(fileSystem);
+}
+
+long DefragBlocks(List<int> fileSystem)
+{
+    (int left, int right) = (0, fileSystem.Count - 1);
+    while (left < right)
+    {
+        if (fileSystem[left] != -1)
+        {
+            left++;
+        }
+        else
+        {
+            if (fileSystem[right] == -1)
+            {
+                right--;
+            }
+            else
+            {
+                (fileSystem[left], fileSystem[right]) = (fileSystem[right], fileSystem[left]);
+            }
+        }
+    }
+
+    return CalculateChecksum(fileSystem);
+}
+
+long CalculateChecksum(List<int> fileSystem)
+{
+    var checksum = 0L;
+    for (var i = 0; i < fileSystem.Count; i++)
+    {
+        var value = fileSystem[i];
+
+        if (value != -1)
+        {
+            checksum += value * i;
+        }
+
+    }
+
+    return checksum;
+}
+
+(List<int>, List<(int Id, int Length, int Position)>, List<(int Length, int Position)>) GenerateFileSystem(string diskMapDescription)
+{
+
+    var file = true;
+    var fileSystem = new List<int>();
+    var freeSpace = new List<(int Length, int Position)>();
+    var files = new List<(int Id, int Length, int Position)>();
+    var id = 0;
+
+    foreach (var length in diskMapDescription.Select(c => int.Parse(c + "")))
+    {
+        var value = file ? id : -1;
+        var position = fileSystem.Count;
+
+        if (file)
+        {
+            files.Add((id, length, position));
+            id += 1;
+        }
+        else
+        {
+            freeSpace.Add((length, position));
+        }
+
+        for (int i = 0; i < length; i++)
+        {
+            fileSystem.Add(value);
+        }
+
+        file = !file;
+    }
+
+    return (fileSystem, files, freeSpace);
+}