exercism/go/nth-prime/nth_prime.go

package prime

var sieve []int

// Nth finds the nth prime and 'true' if the 0th prime wasn't requested
func Nth(n int) (int, bool) {
	if n == 0 {
		return 0, false
	}
	if len(sieve) == 0 {
		// Let's just do some initialization
		sieve = append(sieve, 0)
		sieve = append(sieve, 2)
	}
	sieveLen := len(sieve)
	for i := sieve[len(sieve)-1]; sieveLen <= n; i++ {
		isPrime := true
		for j := 1; j < sieveLen; j++ {
			if i%sieve[j] == 0 {
				isPrime = false
				break
			}
		}
		if isPrime {
			// Found a new prime
			sieve = append(sieve, i)
			sieveLen = len(sieve)
		}
	}
	return sieve[n], true
}