Task

Write a boolean function that tells whether a given integer is prime.



Remember that   1   and all non-positive numbers are not prime.

Use trial division.

Even numbers greater than   2   may be eliminated right away.

A loop from   3   to   √ n    will suffice,   but other loops are allowed.



Related tasks

   count in factors
   prime decomposition
   AKS test for primes
   factors of an integer
   Sieve of Eratosthenes
   factors of a Mersenne number
   trial factoring of a Mersenne number
   partition an integer X into N primes
   sequence of primes by Trial Division


import Foundation
 
extension Int {
  func isPrime() -> Bool {
 
    switch self {
    case let x where x < 2:
      return false
    case 2:
      return true
    default:
      return
        self % 2 != 0 &&
        !stride(from: 3, through: Int(sqrt(Double(self))), by: 2).contains {self % $0 == 0}
    }
  }
}