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  1. using System;
  2. using System.Diagnostics;
  3.  
  4. public class Test
  5. {
  6. 	static bool isPrime(int value)
  7. 	{
  8. 	    for (int divisor = 7; divisor * divisor <= value; divisor += 30)
  9. 	    {
  10. 	        if (value % divisor == 0) { return false; }
  11. 	        if (value % (divisor + 4) == 0) { return false; }
  12. 	        if (value % (divisor + 6) == 0) { return false; }
  13. 	        if (value % (divisor + 10) == 0) { return false; }
  14. 	        if (value % (divisor + 12) == 0) { return false; }
  15. 	        if (value % (divisor + 16) == 0) { return false; }
  16. 	        if (value % (divisor + 22) == 0) { return false; }
  17. 	        if (value % (divisor + 24) == 0) { return false; }
  18. 	    }
  19. 	    return true;
  20. 	}
  21.  
  22. 	public static int getNthPrime( int n )
  23. 	{
  24. 		if ( n == 1 ) return 2;
  25. 		if ( n == 2 ) return 3;
  26. 		if ( n == 3 ) return 5;
  27.  
  28. 		int prime = 7;
  29. 		int i = 3;
  30. 		while ( i < n )
  31. 		{
  32. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  33. 			prime += 4;
  34. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  35. 			prime += 2;
  36. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  37. 			prime += 4;
  38. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  39. 			prime += 2;
  40. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  41. 			prime += 4;
  42. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  43. 			prime += 6;
  44. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  45. 			prime += 2;
  46. 			if ( isPrime( prime ) ) { ++i; if ( i == n ) break; }
  47. 			prime += 6;
  48. 		}
  49. 		return prime;
  50. 	}
  51.  
  52. 	public static void Main()
  53. 	{
  54.         Stopwatch sw = new Stopwatch();
  55.         sw.Start();
  56.         int prime = getNthPrime( 10001 );
  57.         sw.Stop();
  58. 		Console.WriteLine( prime );
  59.         Console.WriteLine( "Time to calculate in milliseconds : {0}",
  60.                             sw.ElapsedMilliseconds );
  61. 	}
  62. }
Success #stdin #stdout 0.07s 24048KB
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Standard input is empty
stdout
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104743
Time to calculate in milliseconds : 15
https://ideone.com/fc4epj
language:
C# (gmcs 5.20.1)
created:
9 years ago
visibility:
public

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