Desafio 11 por @flafmg (#1152)

desafio-11/flafmg/csharp/.valid

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+1798d63d2db6f4967196adc671bbe8b3f

desafio-11/flafmg/csharp/README.MD

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+
+# Desafio 11 - Primos em PI!
+
+
+## pré-requisitos
+
+- [.NET SDK 8.0](https://dotnet.microsoft.com/download/dotnet/8.0)
+
+## compilar e executar
+
+1. **Clone o repositório:**
+   ```bash
+   git clone https://github.com/flafmg/op-desafios.git
+   cd op-desafios/desafio-11/flafmg/csharp
+   ```
+2. **Compile o projeto:**
+   ```bash
+   dotnet build
+   ```
+3. **execute o programa**
+   ```bash
+   dotnet run
+   ```

desafio-11/flafmg/csharp/program.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+
+public class Program
+{
+    public static void Main(string[] args)
+    {
+        if (args.Length < 1)
+        {
+            Console.WriteLine("usio correto: dotnet run <arquivo>");
+            return;
+        }
+
+        var fileName = args[0];
+        if (!File.Exists(fileName))
+        {
+            Console.WriteLine($"arquivo não encontrado: {fileName}");
+            return;
+        }
+
+        var primes = GeneratePrimesUpTo(9973);
+        var biggestSequence = string.Empty;
+        var decimalDigits = ReadDigitsFromFile(fileName);
+
+        for (var i = 0; i < decimalDigits.Length; i++)
+        {
+            var sequence = FindLongestPrimeSequence(primes, decimalDigits, i);
+            if (sequence.Length > biggestSequence.Length)
+            {
+                biggestSequence = sequence;
+            }
+        }
+
+        Console.WriteLine(biggestSequence);
+    }
+    private static HashSet<int> GeneratePrimesUpTo(int limit)
+    {
+        var primes = new HashSet<int>();
+        for (var num = 2; num <= limit; num++)
+        {
+            if (IsPrime(num))
+            {
+                primes.Add(num);
+            }
+        }
+        return primes;
+    }
+    private static bool IsPrime(int number)
+    {
+        if (number < 2) return false;
+        var sqrt = (int)Math.Sqrt(number);
+        for (var i = 2; i <= sqrt; i++)
+        {
+            if (number % i == 0) return false;
+        }
+        return true;
+    }
+    private static string ReadDigitsFromFile(string fileName)
+    {
+        using var reader = new StreamReader(fileName);
+        var content = reader.ReadToEnd();
+
+        var digits = new List<char>();
+        foreach (var ch in content)
+        {
+            if (char.IsDigit(ch))
+            {
+                digits.Add(ch);
+            }
+            else if (ch == '.')
+            {
+                digits.Clear();
+            }
+            else if (!char.IsWhiteSpace(ch))
+            {
+                throw new Exception("arquivo contem caracteres invalidos");
+            }
+        }
+
+        return new string(digits.ToArray());
+    }
+    private static string FindLongestPrimeSequence(HashSet<int> primes, string digits, int startIndex)
+    {
+        var sequence = string.Empty;
+        var longestSequence = string.Empty;
+
+        for (var i = startIndex; i < Math.Min(startIndex + 4, digits.Length); i++)
+        {
+            sequence += digits[i];
+            if (!int.TryParse(sequence, out var number) || !primes.Contains(number)) continue;
+
+            var newSequence = FindLongestPrimeSequence(primes, digits, i + 1);
+            var candidate = sequence + newSequence;
+            if (candidate.Length > longestSequence.Length)
+            {
+                longestSequence = candidate;
+            }
+        }
+
+        return longestSequence;
+    }
+}

desafio-11/flafmg/csharp/program.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <OutputType>Exe</OutputType>
+        <TargetFramework>net8.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+    </PropertyGroup>
+
+</Project>