improved time complexity from exponential to linear time

AdventOfCode2025/AdventOfCode2025.csproj

@@ -20,6 +20,10 @@
       <Content Include="Input\DayTwo.txt">
         <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       </Content>
+      <None Remove="Input\DayThree.txt" />
+      <Content Include="Input\DayThree.txt">
+        <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+      </Content>
     </ItemGroup>
 
 </Project>

AdventOfCode2025/Lobby.cs

@@ -0,0 +1,35 @@
+using System.Runtime.InteropServices.JavaScript;
+using AdventOfCode2025.Utils;
+
+namespace AdventOfCode2025;
+
+public class Lobby : IAdventSolution
+{
+    public AdventSolution Solve(string input)
+    {
+        var lines = input.SplitLines();
+        var total = 0;
+        foreach (var line in lines)
+        {
+            var first = '0';
+            var second = '0';
+            for (var i = 0; i < line.Length; i++)
+            {
+                if (i != line.Length - 1 && line[i] > first)
+                {
+                    first = line[i];
+                    second = line[i + 1];
+                }
+                else if (line[i] > second)
+                {
+                    second = line[i];
+                }
+            }
+            
+            
+            total += int.Parse($"{first}{second}");
+        }
+        
+        return new AdventSolution(total.ToString(), null);
+    }
+}

AdventOfCode2025/Program.cs

@@ -7,3 +7,6 @@ AdventSolver<SecretEntrance>.Solve(dayOneInput, 1, "Secret Entrance");
 
 var dayTwoInput = await File.ReadAllTextAsync("./Input/DayTwo.txt");
 AdventSolver<GiftShop>.Solve(dayTwoInput, 2, "Gift Shop");
+
+var dayThreeInput = await File.ReadAllTextAsync("./Input/DayThree.txt");
+AdventSolver<Lobby>.Solve(dayThreeInput, 3, "Lobby");

AdventOfCode2025/SecretEntrance.cs

@@ -1,10 +1,12 @@
-namespace AdventOfCode2025;
+using AdventOfCode2025.Utils;
+
+namespace AdventOfCode2025;
 
 public class SecretEntrance : IAdventSolution
 {
     public AdventSolution Solve(string input)
     {
-        var lines = input.Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+        var lines = input.SplitLines();
         
         var current = 50;
         var password = 0;

AdventOfCode2025/Utils/StringExtensions.cs

@@ -0,0 +1,9 @@
+namespace AdventOfCode2025.Utils;
+
+public static class StringExtensions
+{
+    public static string[] SplitLines(this string input)
+    {
+        return input.Split('\n', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+    }
+}