Add day 9

Days/Day9.cs

@@ -0,0 +1,181 @@
+using System.Collections.Frozen;
+using System.Numerics;
+using Spectre.Console;
+
+namespace AdventOfCode.Days;
+
+public class Day9 : Day
+{
+    public override int Number => 9;
+    public override string Name => "Disk Fragmenter";
+
+    public override void RunPart1(bool display = true)
+    {
+        var (blocks, freeBlocksStarts) = ParseDiskBlocks();
+
+        var nextFreeIndex = freeBlocksStarts.Dequeue();
+
+        for (var i = blocks.Count - 1; i >= 0; i--)
+        {
+            // There is no more available space to move blocks into on the left
+            if (nextFreeIndex >= i)
+            {
+                break;
+            }
+
+            if (blocks[i] is -1)
+            {
+                continue;
+            }
+
+            blocks[nextFreeIndex] = blocks[i];
+            blocks[i] = -1;
+
+            nextFreeIndex++;
+
+            // Go to next free blocks if current free block is full
+            if (blocks[nextFreeIndex] is not -1)
+            {
+                nextFreeIndex = freeBlocksStarts.Dequeue();
+            }
+        }
+
+        var checksum = blocks
+            .Select((block, index) => block is -1 ? 0 : (long)block * index)
+            .Sum();
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Filesystem checksum: [yellow]{checksum}[/][/]");
+        }
+    }
+
+    public override void RunPart2(bool display = true)
+    {
+        var (blocks, freeBlocks) = ParseDiskBlocks2();
+
+        var mapStart = string.Join(" ", blocks);
+
+        for (var i = blocks.Count - 1; i >= 0; i--)
+        {
+            if (blocks[i] is -1)
+            {
+                continue;
+            }
+
+            // Get file length
+            var fileId = blocks[i];
+            var endPosition = i;
+            var startPosition = i;
+
+            while (startPosition > 0 && blocks[startPosition - 1] == fileId)
+            {
+                startPosition--;
+            }
+
+            var length = (endPosition - startPosition) + 1;
+
+            // Find first available free block on the left
+            var freeBlockIndex = freeBlocks.FindIndex(b => b.StartIndex < startPosition && b.Length >= length);
+
+            if (freeBlockIndex is not -1)
+            {
+                var freeBlock = freeBlocks[freeBlockIndex];
+
+                for (var offset = 0; offset < length; offset++)
+                {
+                    blocks[freeBlock.StartIndex + offset] = blocks[startPosition + offset];
+                    blocks[startPosition + offset] = -1;
+                }
+
+                // Update free block start and length
+                freeBlocks[freeBlockIndex] = (freeBlock.StartIndex + length, freeBlock.Length - length);
+            }
+
+            // Move to next file or free block
+            i = startPosition;
+        }
+
+        var mapEnd = string.Join(" ", blocks).Replace("-1", ".");
+
+        var checksum = blocks
+            .Select((block, index) => block is -1 ? 0 : (long)block * index)
+            .Sum();
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Filesystem checksum: [yellow]{checksum}[/][/]");
+        }
+    }
+
+    private (List<int> Blocks, Queue<int> FreeBlocksStarts) ParseDiskBlocks()
+    {
+        var blocks = new List<int>(20_000 * 10);
+        var freeBlocksStarts = new Queue<int>();
+
+        var readingBlock = true;
+        var blockId = 0;
+
+        foreach (var length in Input.Select(encoded => encoded - '0'))
+        {
+            if (readingBlock)
+            {
+                for (var i = 0; i < length; i++)
+                {
+                    blocks.Add(blockId);
+                }
+
+                blockId++;
+            }
+            else if (length > 0)
+            {
+                freeBlocksStarts.Enqueue(blocks.Count);
+
+                for (var i = 0; i < length; i++)
+                {
+                    blocks.Add(-1);
+                }
+            }
+
+            readingBlock = !readingBlock;
+        }
+
+        return (blocks, freeBlocksStarts);
+    }
+
+    private (List<int> Blocks, List<(int StartIndex, int Length)> FreeBlocks) ParseDiskBlocks2()
+    {
+        var blocks = new List<int>(20_000 * 10);
+        var freeBlocksStarts = new List<(int StartIndex, int Length)>();
+
+        var readingBlock = true;
+        var blockId = 0;
+
+        foreach (var length in Input.Select(encoded => encoded - '0'))
+        {
+            if (readingBlock)
+            {
+                for (var i = 0; i < length; i++)
+                {
+                    blocks.Add(blockId);
+                }
+
+                blockId++;
+            }
+            else if (length > 0)
+            {
+                freeBlocksStarts.Add((blocks.Count, length));
+
+                for (var i = 0; i < length; i++)
+                {
+                    blocks.Add(-1);
+                }
+            }
+
+            readingBlock = !readingBlock;
+        }
+
+        return (blocks, freeBlocksStarts);
+    }
+
+}