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  1. using System;
  2. using System.Collections.Generic;
  3. using System.Diagnostics;
  4.  
  5. public class Test
  6. {
  7.         public static void Main()
  8.         {
  9.             var pgm = new Test();
  10.             pgm.DoStuff();
  11.             Console.WriteLine("Done. Press Enter.");
  12.             Console.ReadLine();
  13.         }
  14.  
  15.         private void DoStuff()
  16.         {
  17.             const int MaxPrime = 
  18.                 1000000; 
  19.                 // 22307;
  20.             for (var i = 0; i < 2; ++i)
  21.             {
  22.                 var sw = Stopwatch.StartNew();
  23.                 var primes = FindPrimes(MaxPrime);
  24.                 sw.Stop();
  25.                 var ms = (1000.0*sw.ElapsedTicks)/Stopwatch.Frequency;
  26.                 Console.WriteLine("{0:N0} primes found in {1} ms ({2})", primes.Count, ms, sw.ElapsedMilliseconds);
  27.             }
  28.             Console.WriteLine();
  29.         }
  30.  
  31.         private List<int> FindPrimes(int maxVal)
  32.         {
  33.             var primes = new List<int>{2};
  34.             for (var x = 3; x <= maxVal; x += 2 )
  35.             {
  36.                 var maxDiv = (int) Math.Round(Math.Sqrt(x));
  37.                 bool isPrime = true;
  38.                 for (var i = 1; i < primes.Count && primes[i] <= maxDiv; ++i)
  39.                 {
  40.                     if ((x%primes[i]) == 0)
  41.                     {
  42.                         isPrime = false;
  43.                         break;
  44.                     }
  45.                 }
  46.                 if (isPrime)
  47.                 {
  48.                     primes.Add(x);
  49.                 }
  50.             }
  51.             return primes;
  52.         }
  53. }
Success #stdin #stdout 1.02s 37184KB
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stdin
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Standard input is empty
stdout
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78,498 primes found in 471.6898 ms (471)
78,498 primes found in 514.6837 ms (514)

Done. Press Enter.
https://ideone.com/sA0DU7
language:
C# (gmcs 5.20.1)
created:
11 years ago
visibility:
public

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