prime.go

package go_kata

import (
	"math"
	"math/big"
)

// Just a test implementation of the function that checks if a number is prime.
func IsPrime(n int) bool {
	// Handle edge cases
	if n <= 1 {
		return false
	}
	if n == 2 || n == 3 {
		return true
	}
	// Any number divisible by 2 or 3 (other than 2 and 3 themselves) is not prime.
	if n%2 == 0 || n%3 == 0 {
		return false
	}

	// Check for factors from 5 to sqrt(n)
	sqrtN := int(math.Sqrt(float64(n)))
	for i := 5; i <= sqrtN; i += 6 {
		if n%i == 0 || n%(i+2) == 0 {
			return false
		}
	}
	return true
}

// Just a test implementation of the function that checks if a number is prime using the math library.
func IsPrimeWithMathLib(n int) bool {

	bigN := big.NewInt(int64(n))
	return bigN.ProbablyPrime(0)
}

// Returns the next prime number that is greater than n.
func GetPrimeThatIsGreaterThan(n int) int {
	for i := n + 1; ; i++ {
		if IsPrime(i) {
			return i
		}
	}
}