2024 Day09 Solved - very ugly and slow, but I know what to do to fix …

…this
smabuk · Dec 9, 2024 · eb4059f · eb4059f
1 parent 85a206b
commit eb4059f
Show file tree

Hide file tree

Showing 2 changed files with 77 additions and 4 deletions.
diff --git a/Solutions/2024/Day09.cs b/Solutions/2024/Day09.cs
@@ -9,8 +9,8 @@ public partial class Day09 {
 
 	public static long Part1(string[] input)
 	{
-		string densediskMap = input[0];
-		List<int> diskMapAsInts = [.. densediskMap.AsDigits<int>()];
+		string denseDiskMap = input[0];
+		List<int> diskMapAsInts = [.. denseDiskMap.AsDigits<int>()];
 		int blockCount = diskMapAsInts.Sum();
 
 		List<int> diskMap = new (blockCount);
@@ -60,12 +60,76 @@ public static long Part1(string[] input)
 		return checkSum;
 	}
 
-	public static string Part2(string[] input) => NO_SOLUTION_WRITTEN_MESSAGE;
+	public static long Part2(string[] input)
+	{
+		string denseDiskMap = input[0];
+		List<int> diskMapAsInts = [.. denseDiskMap.AsDigits<int>()];
+		int blockCount = diskMapAsInts.Sum();
+
+		List<Block> diskMap = [];
+
+		bool fileOrFreeSpace = FILE;
+		int blockNo = 0;
+		int maxBlockNo = 0;
+		foreach (int item in diskMapAsInts) {
+			if (fileOrFreeSpace is FILE) {
+				maxBlockNo = blockNo;
+				diskMap.Add(new Block(blockNo++, item));
+				fileOrFreeSpace = FREE_SPACE;
+			} else {
+				diskMap.Add(new Block(EMPTY, item));
+				fileOrFreeSpace = FILE;
+			}
+		}
+
+
+		// Defragment
+		for (blockNo = maxBlockNo; blockNo > 0; blockNo--) {
+			int blockPtr = diskMap.FindIndex(b => b.Id == blockNo);
+			Block fileBlock = diskMap[blockPtr];
+			int firstFreeSpace = diskMap.FindIndex(b => b.Id == EMPTY && b.BlockSize >= fileBlock.BlockSize);
+			if (blockPtr > firstFreeSpace && firstFreeSpace > 0) {
+				if (diskMap[blockPtr - 1].Id is EMPTY) {
+					diskMap[blockPtr - 1] = diskMap[blockPtr - 1] with { BlockSize = diskMap[blockPtr - 1].BlockSize + fileBlock.BlockSize };
+					diskMap.RemoveAt(blockPtr);
+				} else {
+					diskMap[blockPtr] = fileBlock with { Id = EMPTY };
+				}
+				Block freeSpaceBlock = diskMap[firstFreeSpace];
+				diskMap[firstFreeSpace] = freeSpaceBlock with { BlockSize = freeSpaceBlock.BlockSize - fileBlock.BlockSize };
+				diskMap.Insert(firstFreeSpace, fileBlock);
+			}
+			for (int i = diskMap.Count - 1; i > 0; i--) {
+				if (diskMap[i].Id is EMPTY && diskMap[i - 1].Id is EMPTY) {
+					diskMap[i - 1] = diskMap[i - 1] with { BlockSize = diskMap[i - 1].BlockSize + diskMap[i].BlockSize };
+					diskMap.RemoveAt(i);
+				}
+
+			}
+		}
+
+		_ = diskMap.RemoveAll(b => b.BlockSize is 0);
+
+		long checkSum = 0;
+		int idx = 0;
+		for (int i = 0; i < diskMap.Count; i++) {
+			if (diskMap[i].Id is not EMPTY) {
+				for (int j = 0; j < diskMap[i].BlockSize; j++) {
+					checkSum += diskMap[i].Id * idx++;
+				}
+			} else {
+				idx += diskMap[i].BlockSize;
+			}
+		}
+
 
+		return checkSum;
+	}
 
-	private sealed record Block(int id, int BlockSize);
+	private sealed record Block(int Id, int BlockSize);
 
 	private const bool FILE = true;
 	private const bool FREE_SPACE = false;
 	private const int EMPTY = int.MinValue;
+	private const int NOT_FOUND = -1;
 }
diff --git a/Tests/2024/Tests_09.cs b/Tests/2024/Tests_09.cs
@@ -17,6 +17,15 @@ public async Task Part1(string input, int expected)
 		await Task.Delay(500);
 	}
 
+	[Theory]
+	[InlineData(TEST_DATA, 2858)]
+	public async Task Part2(string input, int expected)
+	{
+		_ = int.TryParse(SolutionRouter.SolveProblem(YEAR, DAY, PART2, input, new Action<string[], bool>(Callback)), out int actual);
+		actual.ShouldBe(expected);
+		await Task.Delay(500);
+	}
+
 
 	private void Callback(string[] lines, bool _)
 	{