public void SieveOfEratosthenes_10_ReturnsExpectedListOfPrimes()
{
// Arrange
var max = 10;
var expectedListOfPrimes = new List <int> {
2, 3, 5, 7
};
// Act
var result = PrimeHelper.SieveOfEratosthenes(max);
// Result
result.Should().BeEquivalentTo(expectedListOfPrimes);
}
private void ComputeCandidateConcatenationPrimesForAllPrimesUpToUpperBound()
{
// If two different primes have sums which are 1 and 2 modulo 3,
// then concatening them yields a number which sum is 0 modulo 3.
// Hence this concatenation is divisble by 3, so not a prime.
// Thus it suffices to consider these cases separately.
// Note that 3 can belong to both of these groups, so it is also treated separately.
var primes = PrimeHelper.SieveOfEratosthenes(UPPER_BOUND_OF_PRIMES).Select(prime => (int)prime);
var firstPrimeGroup = primes.Where(prime => NumberHelper.SumOfDigits(prime) % 3 == 1);
var secondPrimeGroup = primes.Where(prime => NumberHelper.SumOfDigits(prime) % 3 == 2);
ComputeCandidateConcatenations(firstPrimeGroup.ToList());
ComputeCandidateConcatenations(secondPrimeGroup.ToList());
ComputeCandidateConcatenations(3, primes.ToList());
}
public long ComputeSolution()
{
return(PrimeHelper.SieveOfEratosthenes(UPPER_BOUND).Sum());
}