Solved Day 4

Day_4/Day_4.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Day_4", "Day_4\Day_4.csproj", "{F3B089A1-1DCA-4655-99E0-32E1237FFF21}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{F3B089A1-1DCA-4655-99E0-32E1237FFF21}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{F3B089A1-1DCA-4655-99E0-32E1237FFF21}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{F3B089A1-1DCA-4655-99E0-32E1237FFF21}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{F3B089A1-1DCA-4655-99E0-32E1237FFF21}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

Day_4/Day_4/Day_4.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net7.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+    <ItemGroup>
+      <None Update="test.txt">
+        <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      </None>
+      <None Update="data.txt">
+        <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      </None>
+    </ItemGroup>
+
+</Project>

Day_4/Day_4/Program.cs

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+
+const string DATA_FILE = "data.txt";
+
+var lines = ReadData();
+var card_copies = new int[lines.Count()];
+Array.Fill(card_copies, 1);
+
+var sum = 0;
+var card_sum = 0;
+
+for (var i = 0; i < lines.Count(); i++)
+{
+    var score = 0;
+
+    var card = lines[i].Split(":", StringSplitOptions.RemoveEmptyEntries);
+    var numbers = card[1].Split("|", StringSplitOptions.RemoveEmptyEntries);
+    var win_numbers = numbers[0].Split(" ", StringSplitOptions.RemoveEmptyEntries);
+    var player_numbers = numbers[1].Split(" ", StringSplitOptions.RemoveEmptyEntries);
+
+    var matches = player_numbers.Where(p => win_numbers.Contains(p));
+
+    switch (matches.Count())
+    {
+        case 0:
+            score = 0;
+            break;
+        case 1:
+            score = 1;
+            break;
+        default:
+            score = (int)Math.Pow(2, matches.Count() - 1);
+            break;
+    }
+
+    sum += score;
+
+    for (int j = 0; j < card_copies[i]; j++)
+    {
+        for (int k = 1; k <= matches.Count(); k++)
+        {
+            card_copies[(i + k) >= card_copies.Length ? card_copies.Length - 1 : i + k] += 1;
+        }
+    }
+
+    card_sum += card_copies[i];
+}
+
+Console.WriteLine($"Total Score is {sum}");
+Console.WriteLine($"Total Number of Card Copies is {card_sum}"); // 8063216
+
+List<string> ReadData()
+{
+    var data = File.ReadAllLines(DATA_FILE).ToList();
+
+    return data;
+}

Day_4/Day_4/test.txt

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+Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11