diff --git a/AdventOfCode.lpi b/AdventOfCode.lpi
index 8cebdb5..f9cc1bf 100644
--- a/AdventOfCode.lpi
+++ b/AdventOfCode.lpi
@@ -81,6 +81,10 @@
         <Filename Value="solvers\UCosmicExpansion.pas"/>
         <IsPartOfProject Value="True"/>
       </Unit>
+      <Unit>
+        <Filename Value="solvers\UHotSprings.pas"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
     </Units>
   </ProjectOptions>
   <CompilerOptions>
diff --git a/AdventOfCode.lpr b/AdventOfCode.lpr
index 9bda50e..5d88d23 100644
--- a/AdventOfCode.lpr
+++ b/AdventOfCode.lpr
@@ -26,7 +26,7 @@ uses
   Classes, SysUtils, CustApp,
   USolver,
   UTrebuchet, UCubeConundrum, UGearRatios, UScratchcards, UGiveSeedFertilizer, UWaitForIt, UCamelCards,
-  UHauntedWasteland, UNumberTheory, UMirageMaintenance, UPipeMaze, UCosmicExpansion;
+  UHauntedWasteland, UNumberTheory, UMirageMaintenance, UPipeMaze, UCosmicExpansion, UHotSprings;
 
 type
 
@@ -62,6 +62,7 @@ begin
   engine.RunAndFree(TMirageMaintenance.Create);
   engine.RunAndFree(TPipeMaze.Create);
   engine.RunAndFree(TCosmicExpansion.Create);
+  engine.RunAndFree(THotSprings.Create);
   engine.Free;
 end;
 
diff --git a/solvers/UHotSprings.pas b/solvers/UHotSprings.pas
new file mode 100644
index 0000000..6b27105
--- /dev/null
+++ b/solvers/UHotSprings.pas
@@ -0,0 +1,170 @@
+{
+  Solutions to the Advent Of Code.
+  Copyright (C) 2023  Stefan Müller
+
+  This program is free software: you can redistribute it and/or modify it under
+  the terms of the GNU General Public License as published by the Free Software
+  Foundation, either version 3 of the License, or (at your option) any later
+  version.
+
+  This program is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  this program.  If not, see <http://www.gnu.org/licenses/>.
+}
+
+unit UHotSprings;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, Generics.Collections, USolver;
+
+const
+  COperationalChar = '.';
+  CDamagedChar = '#';
+  CWildcardChar = '?';
+  COperationalPatternChars = [COperationalChar, CWildcardChar];
+  CDamagedPatternChars = [CDamagedChar, CWildcardChar];
+
+type
+
+  { THotSprings }
+
+  THotSprings = class(TSolver)
+  private
+    FValidation: specialize TList<Integer>;
+    FSpringPattern: string;
+    procedure ExtendArrangement(const AArrangement: string; const ARemainingFreeOperationalCount, ACurrentValidationIndex:
+      Integer);
+    function TryAppendOperationalChar(var AArrangement: string): Boolean;
+    function TryAppendValidationBlock(var AArrangement: string; const ALength: Integer): Boolean;
+  public
+    constructor Create;
+    destructor Destroy; override;
+    procedure ProcessDataLine(const ALine: string); override;
+    procedure Finish; override;
+    function GetDataFileName: string; override;
+    function GetPuzzleName: string; override;
+  end;
+
+implementation
+
+{ THotSprings }
+
+procedure THotSprings.ExtendArrangement(const AArrangement: string; const ARemainingFreeOperationalCount,
+  ACurrentValidationIndex: Integer);
+var
+  i, len: Integer;
+  match: Boolean;
+  temp: string;
+begin
+  len := Length(AArrangement);
+  if len = Length(FSpringPattern) then
+    Inc(FPart1)
+  else begin
+    temp := AArrangement;
+    // Tries to append a dot (operational) to the current arrangement.
+    if (ARemainingFreeOperationalCount > 0) and TryAppendOperationalChar(temp) then
+    begin
+      ExtendArrangement(temp, ARemainingFreeOperationalCount - 1, ACurrentValidationIndex);
+    end;
+
+    // Tries to append the current validation block (damaged) to the current arrangement.
+    if ACurrentValidationIndex < FValidation.Count then
+    begin
+      temp := AArrangement;
+      match := TryAppendValidationBlock(temp, FValidation[ACurrentValidationIndex]);
+
+      // ... and the mandatory dot after the block, if it is not the last block.
+      if match
+      and (ACurrentValidationIndex < FValidation.Count - 1)
+      and not TryAppendOperationalChar(temp) then
+        match := False;
+
+      if match then
+        ExtendArrangement(temp, ARemainingFreeOperationalCount, ACurrentValidationIndex + 1);
+    end;
+  end;
+end;
+
+function THotSprings.TryAppendOperationalChar(var AArrangement: string): Boolean;
+begin
+  if FSpringPattern[Length(AArrangement) + 1] in COperationalPatternChars then
+  begin
+    AArrangement := AArrangement + COperationalChar;
+    Result := True;
+  end
+  else
+    Result := False;
+end;
+
+function THotSprings.TryAppendValidationBlock(var AArrangement: string; const ALength: Integer): Boolean;
+var
+  i, len: Integer;
+begin
+  Result := True;
+  len := Length(AArrangement);
+  for i := 1 to ALength do
+  begin
+    if FSpringPattern[len + i] in CDamagedPatternChars then
+      AArrangement := AArrangement + CDamagedChar
+    else begin
+      Result := False;
+      Break;
+    end;
+  end;
+end;
+
+constructor THotSprings.Create;
+begin
+  FValidation := specialize TList<Integer>.Create;
+end;
+
+destructor THotSprings.Destroy;
+begin
+  FValidation.Free;
+  inherited Destroy;
+end;
+
+procedure THotSprings.ProcessDataLine(const ALine: string);
+var
+  split: TStringArray;
+  i, val, maxFreeOperationalCount: Integer;
+begin
+  FValidation.Clear;
+  split := ALine.Split([' ', ',']);
+  FSpringPattern := split[0];
+
+  maxFreeOperationalCount := Length(FSpringPattern) - Length(split) + 2;
+  for i := 1 to Length(split) - 1 do
+  begin
+    val := StrToInt(split[i]);
+    FValidation.Add(val);
+    Dec(maxFreeOperationalCount, val);
+  end;
+
+  ExtendArrangement('', maxFreeOperationalCount, 0);
+end;
+
+procedure THotSprings.Finish;
+begin
+
+end;
+
+function THotSprings.GetDataFileName: string;
+begin
+  Result := 'hot_springs.txt';
+end;
+
+function THotSprings.GetPuzzleName: string;
+begin
+  Result := 'Day 12: Hot Springs';
+end;
+
+end.
+
diff --git a/tests/AdventOfCodeFPCUnit.lpi b/tests/AdventOfCodeFPCUnit.lpi
index 3875c21..178fda6 100644
--- a/tests/AdventOfCodeFPCUnit.lpi
+++ b/tests/AdventOfCodeFPCUnit.lpi
@@ -88,6 +88,10 @@
         <Filename Value="UCosmicExpansionTestCases.pas"/>
         <IsPartOfProject Value="True"/>
       </Unit>
+      <Unit>
+        <Filename Value="UHotSpringsTestCases.pas"/>
+        <IsPartOfProject Value="True"/>
+      </Unit>
     </Units>
   </ProjectOptions>
   <CompilerOptions>
diff --git a/tests/AdventOfCodeFPCUnit.lpr b/tests/AdventOfCodeFPCUnit.lpr
index 3a607b4..896d2ac 100644
--- a/tests/AdventOfCodeFPCUnit.lpr
+++ b/tests/AdventOfCodeFPCUnit.lpr
@@ -5,7 +5,8 @@ program AdventOfCodeFPCUnit;
 uses
   Interfaces, Forms, GuiTestRunner, USolver, UBaseTestCases, UTrebuchetTestCases, UCubeConundrumTestCases,
   UGearRatiosTestCases, UScratchcardsTestCases, UGiveSeedFertilizerTestCases, UWaitForItTestCases, UCamelCardsTestCases,
-  UHauntedWastelandTestCases, UMirageMaintenanceTestCases, UPipeMazeTestCases, UCosmicExpansionTestCases;
+  UHauntedWastelandTestCases, UMirageMaintenanceTestCases, UPipeMazeTestCases, UCosmicExpansionTestCases, 
+  UHotSpringsTestCases;
 
 {$R *.res}
 
diff --git a/tests/UHotSpringsTestCases.pas b/tests/UHotSpringsTestCases.pas
new file mode 100644
index 0000000..1822c8c
--- /dev/null
+++ b/tests/UHotSpringsTestCases.pas
@@ -0,0 +1,139 @@
+{
+  Solutions to the Advent Of Code.
+  Copyright (C) 2023  Stefan Müller
+
+  This program is free software: you can redistribute it and/or modify it under
+  the terms of the GNU General Public License as published by the Free Software
+  Foundation, either version 3 of the License, or (at your option) any later
+  version.
+
+  This program is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+  FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along with
+  this program.  If not, see <http://www.gnu.org/licenses/>.
+}
+
+unit UHotSpringsTestCases;
+
+{$mode ObjFPC}{$H+}
+
+interface
+
+uses
+  Classes, SysUtils, fpcunit, testregistry, USolver, UBaseTestCases, UHotSprings;
+
+type
+
+  { THotSpringsFullDataTestCase }
+
+  THotSpringsFullDataTestCase = class(TEngineBaseTest)
+  protected
+    function CreateSolver: ISolver; override;
+  published
+    procedure TestPart1;
+  end;
+
+  { THotSpringsExampleTestCase }
+
+  THotSpringsExampleTestCase = class(TExampleEngineBaseTest)
+  protected
+    function CreateSolver: ISolver; override;
+  published
+    procedure TestPart1;
+  end;
+
+  { THotSpringsTestCase }
+
+  THotSpringsTestCase = class(TSolverTestCase)
+  protected
+    function CreateSolver: ISolver; override;
+    procedure TestSingleLine(const ALine: string; const AValue: Integer);
+  published
+    procedure TestExampleLine1;
+    procedure TestExampleLine2;
+    procedure TestExampleLine3;
+    procedure TestExampleLine4;
+    procedure TestExampleLine5;
+    procedure TestExampleLine6;
+  end;
+
+implementation
+
+{ THotSpringsFullDataTestCase }
+
+function THotSpringsFullDataTestCase.CreateSolver: ISolver;
+begin
+  Result := THotSprings.Create;
+end;
+
+procedure THotSpringsFullDataTestCase.TestPart1;
+begin
+  AssertEquals(7344, FSolver.GetResultPart1);
+end;
+
+{ THotSpringsExampleTestCase }
+
+function THotSpringsExampleTestCase.CreateSolver: ISolver;
+begin
+  Result := THotSprings.Create;
+end;
+
+procedure THotSpringsExampleTestCase.TestPart1;
+begin
+  AssertEquals(21, FSolver.GetResultPart1);
+end;
+
+{ THotSpringsTestCase }
+
+function THotSpringsTestCase.CreateSolver: ISolver;
+begin
+  Result := THotSprings.Create;
+end;
+
+procedure THotSpringsTestCase.TestSingleLine(const ALine: string; const AValue: Integer);
+begin
+  FSolver.Init;
+  FSolver.ProcessDataLine(ALine);
+  FSolver.Finish;
+  AssertEquals(AValue, FSolver.GetResultPart1);
+end;
+
+procedure THotSpringsTestCase.TestExampleLine1;
+begin
+  TestSingleLine('???.### 1,1,3', 1);
+end;
+
+procedure THotSpringsTestCase.TestExampleLine2;
+begin
+  TestSingleLine('.??..??...?##. 1,1,3', 4);
+end;
+
+procedure THotSpringsTestCase.TestExampleLine3;
+begin
+  TestSingleLine('?#?#?#?#?#?#?#? 1,3,1,6', 1);
+end;
+
+procedure THotSpringsTestCase.TestExampleLine4;
+begin
+  TestSingleLine('????.#...#... 4,1,1', 1);
+end;
+
+procedure THotSpringsTestCase.TestExampleLine5;
+begin
+  TestSingleLine('????.######..#####. 1,6,5', 4);
+end;
+
+procedure THotSpringsTestCase.TestExampleLine6;
+begin
+  TestSingleLine('?###???????? 3,2,1', 10);
+end;
+
+initialization
+
+  RegisterTest(THotSpringsFullDataTestCase);
+  RegisterTest(THotSpringsExampleTestCase);
+  RegisterTest(THotSpringsTestCase);
+end.
+