feat: solved day 9 part 2

09/DiskFragmenter.Tests/DiskMapTests.cs

@@ -4,6 +4,11 @@ public class DiskMapTests
 {
   private const string TestInput = "12345";
   private const string ExampleInput = "2333133121414131402";
+
+  private async Task<string> GetPuzzleInput()
+  {
+    return await File.ReadAllTextAsync(Path.Combine(AppContext.BaseDirectory, "INPUT.txt"));
+  }
   
   [Test]
   public async Task FromDenseFormat_WhenCalled_ItShouldReturnDiskMap()
@@ -59,4 +64,48 @@ public class DiskMapTests
 
     await Assert.That(result).IsEqualTo(1928);
   }
+  
+  [Test]
+  public async Task CalculateCheckSum_WhenCalledWithPuzzleInput_ItShouldReturnExpectedValue()
+  {
+    var input = await GetPuzzleInput();
+    
+    var result = DiskMap.FromDenseFormat(input)
+      .CompactDisk()
+      .CalculateCheckSum();
+
+    await Assert.That(result).IsEqualTo(6200294120911);
+  }
+  
+  [Test]
+  public async Task CalculateCheckSum_WhenCalledWhenCalledWithTestInputAndNoFragmentation_ItShouldReturnExpectedValue()
+  {
+    var result = DiskMap.FromDenseFormat(TestInput)
+      .CompactDiskWithoutFragmentation()
+      .CalculateCheckSum();
+
+    await Assert.That(result).IsEqualTo(132);
+  }
+
+  [Test]
+  public async Task CalculateCheckSum_WhenCalledWithExampleInputAndNoFragmentation_ItShouldReturnExpectedValue()
+  {
+    var result = DiskMap.FromDenseFormat(ExampleInput)
+      .CompactDiskWithoutFragmentation()
+      .CalculateCheckSum();
+
+    await Assert.That(result).IsEqualTo(2858);
+  }
+  
+  [Test]
+  public async Task CalculateCheckSum_WhenCalledWithPuzzleInputAndNoFragmentation_ItShouldReturnExpectedValue()
+  {
+    var input = await GetPuzzleInput();
+    
+    var result = DiskMap.FromDenseFormat(input)
+      .CompactDiskWithoutFragmentation()
+      .CalculateCheckSum();
+
+    await Assert.That(result).IsEqualTo(6227018762750);
+  }
 }

09/DiskFragmenter/Program.cs

@@ -18,7 +18,12 @@ var input = await File.ReadAllTextAsync(args[0]);
 var stopwatch = new Stopwatch();
 stopwatch.Start();
 
-var result = DiskMap.FromDenseFormat(input).CompactDisk().CalculateCheckSum();
+var map = DiskMap.FromDenseFormat(input);
+var compactedMap = isPart2
+  ? map.CompactDiskWithoutFragmentation()
+  : map.CompactDisk();
+
+var result = compactedMap.CalculateCheckSum();
 
 stopwatch.Stop();
 Console.WriteLine($"The checksum of the compacted disk is {result}. ({stopwatch.ElapsedMilliseconds}ms)");
@@ -54,12 +59,19 @@ class DiskMap
     return total;
   }
 
+  // TODO: Can this be solved without less index manipulation?
+  // Can I create a data structure that suits both ways
+  // of doing disk compaction and allows for easily calculating
+  // the checksum
+  // maybe something like [block]
+  // block needs to represent a block of free space
+  // and a block of file ids
+  // each will consist indexes, value
   public DiskMap CompactDisk()
   {
     var compactedFormat = _expandedFormat.ToList();
     var blockToBeMovedIndex = compactedFormat.Count - 1;
     
-    // TODO: I think this might be easier to deal with in a while loop.
     for (var possiblePlacementIndex = 0; possiblePlacementIndex < compactedFormat.Count; possiblePlacementIndex++)
     {
       if (blockToBeMovedIndex < possiblePlacementIndex)
@@ -93,15 +105,19 @@ class DiskMap
   public DiskMap CompactDiskWithoutFragmentation()
   {
     var compactedFormat = _expandedFormat.ToList();
-
+    
+    // initialize file block pointers
     var fileBlockStartIndex = compactedFormat.FindLastIndex(i => i is not -1);
     var fileBlockEndIndex = fileBlockStartIndex;
     
+    // initialize free block points
     var freeBlockStartIndex = compactedFormat.IndexOf(-1);
     var freeBlockEndIndex = freeBlockStartIndex;
-
+    
+    // loop over all possible file blocks
     while (fileBlockEndIndex > -1)
     {
+      // loop to end of current file block
       while (compactedFormat[fileBlockEndIndex] == compactedFormat[fileBlockStartIndex])
       {
         fileBlockEndIndex--;
@@ -112,42 +128,71 @@ class DiskMap
         }
       }
       
-      while (freeBlockEndIndex < compactedFormat.Count - 1 && freeBlockEndIndex is not -1)
+      // loop over all free blocks that are to the left of the
+      // current file block
+      while (
+        freeBlockEndIndex < compactedFormat.Count - 1 && 
+        freeBlockEndIndex is not -1 &&
+        freeBlockEndIndex < fileBlockEndIndex
+      )
       {
+        // find end of current free block
         while (compactedFormat[freeBlockStartIndex] == compactedFormat[freeBlockEndIndex])
         {
           freeBlockEndIndex++;
         }
 
+        // determine if free block can hold file block
         var fileBlockLength = fileBlockStartIndex - fileBlockEndIndex;
         var freeBlockLength = freeBlockEndIndex - freeBlockStartIndex;
 
-        if (freeBlockLength < fileBlockLength || freeBlockStartIndex > file)
+        if (freeBlockLength < fileBlockLength)
         {
+          // if current free block cannot hold file block
+          // advance to next free block
           freeBlockStartIndex = compactedFormat.IndexOf(-1, freeBlockEndIndex);
           freeBlockEndIndex = freeBlockStartIndex;
           continue;
         }
+        
+        // if current free block can hold file block
+        // loop over the free block positions and place
+        // the file block's id in them, but only replace
+        // as many free blocks as there are file blocks
+        var blockLengthDelta = freeBlockLength - fileBlockLength;
 
-        for (int i = freeBlockStartIndex; i < freeBlockEndIndex; i++)
+        for (var i = freeBlockStartIndex; i < freeBlockEndIndex - blockLengthDelta; i++)
         {
-          for (int j = fileBlockStartIndex; j < fileBlockEndIndex; j++)
-          {
-            var fileIdToMove = compactedFormat[j];
-            compactedFormat[i] = fileIdToMove;
-            compactedFormat[j] = -1;
-          }
+          compactedFormat[i] = compactedFormat[fileBlockStartIndex];
         }
+        
+        // loop over original file block positions
+        // and free them up.
+        for (var j = fileBlockStartIndex; j > fileBlockEndIndex; j--)
+        {
+          compactedFormat[j] = -1;
+        }
+
+        break;
       }
       
+      // if we have reached the end of all
+      // possible file blocks then no
+      // need to go to next file block
+      if (fileBlockEndIndex is -1)
+      {
+        break;
+      }
+      
+      // move to next file block
       fileBlockStartIndex = compactedFormat.FindLastIndex(fileBlockEndIndex, i => i is not -1);
       fileBlockEndIndex = fileBlockStartIndex;
       
+      // reset free block to beginning free block
       freeBlockStartIndex = compactedFormat.IndexOf(-1);
       freeBlockEndIndex = freeBlockStartIndex;
     }
     
-    
     return new(compactedFormat);
   }
   

README.md

@@ -52,3 +52,4 @@ dotnet build
 | 06  | [Problem](./06/PROBLEM.md) | [Solution](./06/GuardGallivant/)       | I kind of brute forced part two...                                                                     |
 | 07  | [Problem](./07/PROBLEM.md) | [Solution](./07/BridgeRepair/)         | Not perfect or pretty, but good enough                                                                 |
 | 08  | [Problem](./08/PROBLEM.md) | [Solution](./08/ResonantCollinearity/) | Without some help from chat I don't know where I'd be...to be fair the description kind of mislead me. |
+| 09  | [Problem](./09/PROBLEM.md) | [Solution](./09/DiskFragmenter/)       | Doing things with indexes is error prone.                                                              |