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public class Semiprime | |
{ | |
static public bool Semiprime1(int number) | |
{ | |
var divisors = new List<int>(); | |
for (var i = 2; i <= Math.Sqrt(number); i++) | |
{ | |
if (number % i == 0) | |
{ | |
divisors.Add(i); | |
divisors.Add(number / i); | |
} | |
} | |
return divisors.Count == 2 && divisors.All(IsPrime); | |
} | |
static public bool Semiprime2(int number) | |
{ | |
var hadTwoDivisors = false; | |
for (var i = 2; i <= Math.Sqrt(number); i++) | |
{ | |
if (number % i == 0) | |
{ | |
if (hadTwoDivisors || !IsPrime(i) || !IsPrime(number / i)) | |
return false; | |
hadTwoDivisors = true; | |
} | |
} | |
return hadTwoDivisors; | |
} | |
static public bool Semiprime3(int number) | |
{ | |
var divisors = GetDivisors(number).ToArray(); | |
return divisors.Count() == 2 && divisors.All(IsPrime); | |
} | |
static public IEnumerable<int> GetDivisors(int number) | |
{ | |
for (var i = 2; i <= Math.Sqrt(number); i++) | |
{ | |
if (number % i == 0) | |
{ | |
yield return i; | |
yield return number / i; | |
} | |
} | |
} | |
private static bool IsPrime(int number) | |
{ | |
if (number == 1) | |
return false; | |
for (var i = 2; i <= Math.Sqrt(number); i++) | |
{ | |
if (number % i == 0) | |
return false; | |
} | |
return true; | |
} | |
} |
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