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  1. object Main {
  2.   /**
  3.    * Checks if a number is prime using optimized trial division
  4.    * @param n The number to check
  5.    * @return true if prime, false otherwise
  6.    */
  7.   def isPrime(n: Int): Boolean = {
  8.     if (n <= 1) false               // 0 and 1 are not primes
  9.     else if (n == 2) true           // 2 is the only even prime
  10.     else if (n % 2 == 0) false      // Eliminate even numbers
  11.     else {
  12.       // Check divisors up to sqrt(n), skipping even numbers
  13.       val maxDivisor = math.sqrt(n).toInt
  14.       (3 to maxDivisor by 2).forall(n % _ != 0)
  15.     }
  16.   }
  17.  
  18.   /**
  19.    * Generates prime numbers up to a limit using Sieve of Eratosthenes
  20.    * @param limit Upper bound for prime generation
  21.    * @return Sequence of primes up to limit
  22.    */
  23.   def sieveOfEratosthenes(limit: Int): Seq[Int] = {
  24.     if (limit < 2) Seq.empty
  25.     else {
  26.       val sieve = Array.fill(limit + 1)(true)
  27.       sieve(0) = false
  28.       sieve(1) = false
  29.  
  30.       for {
  31.         i <- 2 to math.sqrt(limit).toInt
  32.         if sieve(i)
  33.         j <- i * i to limit by i
  34.       } sieve(j) = false
  35.  
  36.       sieve.zipWithIndex.collect { case (true, num) => num }
  37.     }
  38.   }
  39.  
  40.   def main(args: Array[String]): Unit = {
  41.     // Test individual numbers
  42.     val testNumbers = List(2, 3, 17, 25, 997, 1000)
  43.     println("Prime checks:")
  44.     testNumbers.foreach { n =>
  45.       println(f"$n%4d is prime: ${isPrime(n)}%5s")
  46.     }
  47.  
  48.     // Generate primes up to 100
  49.     val primesUpTo100 = sieveOfEratosthenes(100)
  50.     println("\nPrimes up to 100:")
  51.     println(primesUpTo100.mkString(", "))
  52.   }
  53. }
Success #stdin #stdout 0.67s 73564KB
comments (?)
stdin 
Standard input is empty
stdout 
Prime checks:
   2 is prime:  true
   3 is prime:  true
  17 is prime:  true
  25 is prime: false
 997 is prime:  true
1000 is prime: false

Primes up to 100:
2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97
https://ideone.com/3KW23A
language:
Scala (scala 2.12.8)
created:
13 days ago
visibility:
public

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