diff --git a/AdventOfCode2024/AdventOfCode2024.vcxproj b/AdventOfCode2024/AdventOfCode2024.vcxproj
index cbf78e3..7af98e5 100644
--- a/AdventOfCode2024/AdventOfCode2024.vcxproj
+++ b/AdventOfCode2024/AdventOfCode2024.vcxproj
@@ -129,13 +129,13 @@
   </ItemDefinitionGroup>
   <ItemGroup>
     <ClCompile Include="AdventOfCode2024.cpp" />
-    <ClCompile Include="Demo.cpp" />
+    <ClCompile Include="HistorianHysteria.cpp" />
     <ClCompile Include="Program.cpp" />
     <ClCompile Include="Solver.cpp" />
     <ClCompile Include="SolverEngine.cpp" />
   </ItemGroup>
   <ItemGroup>
-    <ClInclude Include="Demo.h" />
+    <ClInclude Include="HistorianHysteria.h" />
     <ClInclude Include="Program.h" />
     <ClInclude Include="Solver.h" />
     <ClInclude Include="SolverEngine.h" />
diff --git a/AdventOfCode2024/AdventOfCode2024.vcxproj.filters b/AdventOfCode2024/AdventOfCode2024.vcxproj.filters
index dc84f48..d9e4eb4 100644
--- a/AdventOfCode2024/AdventOfCode2024.vcxproj.filters
+++ b/AdventOfCode2024/AdventOfCode2024.vcxproj.filters
@@ -18,9 +18,6 @@
     <ClCompile Include="AdventOfCode2024.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
-    <ClCompile Include="Demo.cpp">
-      <Filter>Source Files</Filter>
-    </ClCompile>
     <ClCompile Include="Solver.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
@@ -30,6 +27,9 @@
     <ClCompile Include="Program.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="HistorianHysteria.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="SolverEngine.h">
@@ -38,10 +38,10 @@
     <ClInclude Include="Solver.h">
       <Filter>Header Files</Filter>
     </ClInclude>
-    <ClInclude Include="Demo.h">
+    <ClInclude Include="Program.h">
       <Filter>Header Files</Filter>
     </ClInclude>
-    <ClInclude Include="Program.h">
+    <ClInclude Include="HistorianHysteria.h">
       <Filter>Header Files</Filter>
     </ClInclude>
   </ItemGroup>
diff --git a/AdventOfCode2024/Demo.cpp b/AdventOfCode2024/Demo.cpp
deleted file mode 100644
index ac5bbb6..0000000
--- a/AdventOfCode2024/Demo.cpp
+++ /dev/null
@@ -1,43 +0,0 @@
-// Solutions to the Advent Of Code 2024.
-// Copyright (C) 2024  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/>.
-
-#include "Demo.h"
-
-std::string Demo::getPuzzleName() const
-{
-    return "Demo";
-}
-
-std::string Demo::getInputFileName() const
-{
-    return "demo.txt";
-}
-
-void Demo::processDataLine(const std::string& line)
-{
-    part1 += std::stoi(line);
-    if (part2 == 0)
-    {
-        part2 = std::stoi(line);
-    }
-    else
-    {
-        part2 *= std::stoi(line);
-    }
-}
-
-void Demo::finish()
-{
-}
diff --git a/AdventOfCode2024/HistorianHysteria.cpp b/AdventOfCode2024/HistorianHysteria.cpp
new file mode 100644
index 0000000..babad2f
--- /dev/null
+++ b/AdventOfCode2024/HistorianHysteria.cpp
@@ -0,0 +1,70 @@
+// Solutions to the Advent Of Code 2024.
+// Copyright (C) 2024  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/>.
+
+#include <iostream>
+
+#include "HistorianHysteria.h"
+
+std::string HistorianHysteria::getPuzzleName() const
+{
+    return "Day 1: Historian Hysteria";
+}
+
+std::string HistorianHysteria::getInputFileName() const
+{
+    return "historian_hysteria.txt";
+}
+
+void HistorianHysteria::processDataLine(const std::string& line)
+{
+    auto pos = line.find("   ");
+    left.insert(std::stoi(line.substr(0, pos)));
+    right.insert(std::stoi(line.substr(pos + 3)));
+}
+
+void HistorianHysteria::finish()
+{
+    int prev{ 0 };
+    auto nSame{ 0 };
+    auto leftIterator = left.begin();
+    auto rightIterator = right.begin();
+    auto rightSameIterator = right.begin();
+
+    while (leftIterator != left.end())
+    {
+        part1 += abs(*leftIterator - *rightIterator);
+
+        if (prev != *leftIterator)
+        {
+            nSame = 0;
+            // Skips over numbers in the right list that are smaller than the current left number.
+            while (rightSameIterator != right.end() && *rightSameIterator < *leftIterator)
+            {
+                rightSameIterator++;
+            }
+            // Counts the occurrences of the current left number in the right list.
+            while (rightSameIterator != right.end() && *rightSameIterator == *leftIterator)
+            {
+                rightSameIterator++;
+                nSame++;
+            }
+            prev = *leftIterator;
+        }
+        part2 += *leftIterator * nSame;
+
+        leftIterator++;
+        rightIterator++;
+    }
+}
diff --git a/AdventOfCode2024/Demo.h b/AdventOfCode2024/HistorianHysteria.h
similarity index 90%
rename from AdventOfCode2024/Demo.h
rename to AdventOfCode2024/HistorianHysteria.h
index d17ae03..218743e 100644
--- a/AdventOfCode2024/Demo.h
+++ b/AdventOfCode2024/HistorianHysteria.h
@@ -15,9 +15,11 @@
 
 #pragma once
 
+#include <set>
+
 #include "Solver.h"
 
-class Demo :
+class HistorianHysteria :
     public Solver
 {
 public:
@@ -25,4 +27,7 @@ class Demo :
     virtual std::string getInputFileName() const override;
     virtual void processDataLine(const std::string& line) override;
     virtual void finish() override;
+private:
+    std::multiset<int> left;
+    std::multiset<int> right;
 };
diff --git a/AdventOfCode2024/Program.cpp b/AdventOfCode2024/Program.cpp
index 83908da..70f0ece 100644
--- a/AdventOfCode2024/Program.cpp
+++ b/AdventOfCode2024/Program.cpp
@@ -16,10 +16,11 @@
 #include <iostream>
 #include <memory>
 
-#include "Demo.h"
 #include "Program.h"
 #include "SolverEngine.h"
 
+#include "HistorianHysteria.h"
+
 void Program::run()
 {
     std::cout << "### Advent of Code 2024 ###\n";
@@ -29,7 +30,7 @@ void Program::run()
 void Program::runSolvers()
 {
     SolverEngine solverEngine{ getInputPaths() };
-    solverEngine.run(*std::make_unique<Demo>());
+    solverEngine.run(*std::make_unique<HistorianHysteria>());
 }
 
 std::vector<std::string> Program::getInputPaths() const
diff --git a/AdventOfCode2024/UnitTests/UnitTests.cpp b/AdventOfCode2024/UnitTests/UnitTests.cpp
index 62ad50e..d65336a 100644
--- a/AdventOfCode2024/UnitTests/UnitTests.cpp
+++ b/AdventOfCode2024/UnitTests/UnitTests.cpp
@@ -18,35 +18,36 @@
 
 #include "Part1TestContext.h"
 #include "Part2TestContext.h"
-#include "../Demo.h"
 #include "../Solver.h"
 #include "../SolverEngine.h"
 
+#include "../HistorianHysteria.h"
+
 using namespace Microsoft::VisualStudio::CppUnitTestFramework;
 
 namespace UnitTests
 {
-    TEST_CLASS(DemoTests)
+    TEST_CLASS(HistorianHysteriaTests)
     {
     public:
         TEST_METHOD(FullData1)
         {
-            runTest(*std::make_unique<Demo>(), 66, part1TestContext_);
+            runTest(*std::make_unique<HistorianHysteria>(), 2176849, part1TestContext_);
         }
 
         TEST_METHOD(FullData2)
         {
-            runTest(*std::make_unique<Demo>(), 39916800, part2TestContext_);
+            runTest(*std::make_unique<HistorianHysteria>(), 23384288, part2TestContext_);
         }
 
         TEST_METHOD(ExampleData1)
         {
-            runTest(*std::make_unique<Demo>(), 10, part1ExampleTestContext_);
+            runTest(*std::make_unique<HistorianHysteria>(), 11, part1ExampleTestContext_);
         }
 
         TEST_METHOD(ExampleData2)
         {
-            runTest(*std::make_unique<Demo>(), 24, part2ExampleTestContext_);
+            runTest(*std::make_unique<HistorianHysteria>(), 31, part2ExampleTestContext_);
         }
 
     private:
diff --git a/AdventOfCode2024/UnitTests/UnitTests.vcxproj b/AdventOfCode2024/UnitTests/UnitTests.vcxproj
index 7306324..f4b1153 100644
--- a/AdventOfCode2024/UnitTests/UnitTests.vcxproj
+++ b/AdventOfCode2024/UnitTests/UnitTests.vcxproj
@@ -102,7 +102,7 @@
     <Link>
       <SubSystem>Windows</SubSystem>
       <AdditionalLibraryDirectories>$(VCInstallDir)UnitTest\lib;..\$(Platform)\$(Configuration);D:\Projects\VS\AdventOfCode2024Full\code\AdventOfCode2024\x64\Debug;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
-      <AdditionalDependencies>Demo.obj;Solver.obj;SolverEngine.obj;%(AdditionalDependencies)</AdditionalDependencies>
+      <AdditionalDependencies>Solver.obj;SolverEngine.obj;HistorianHysteria.obj;%(AdditionalDependencies)</AdditionalDependencies>
     </Link>
   </ItemDefinitionGroup>
   <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|Win32'">