/// <summary>
/// Finds greatest prime factor.
/// </summary>
public static long Q003(long n)
{
// n > 1;
List <long> factors = new List <long>();
factors.Add(n);
long sqrt = (long)Math.Floor(Math.Sqrt(n));
for (long i = 2; i <= sqrt; i++)
{
if (n % i == 0)
{
factors.Add(i);
factors.Add(n / i);
}
}
factors.Sort();
for (int i = factors.Count - 1; i >= 0; i--)
{
if (NumberTheory.IsPrime(factors[i]))
{
return(factors[i]);
}
}
return(-1);
}
public void TestIsPrime_Int64()
{
Assert.That(NumberTheory.IsPrime(2), Is.True);
Assert.That(NumberTheory.IsPrime(3), Is.True);
Assert.That(NumberTheory.IsPrime(4), Is.False);
Assert.That(NumberTheory.IsPrime(5), Is.True);
Assert.That(NumberTheory.IsPrime(10), Is.False);
Assert.That(NumberTheory.IsPrime(17), Is.True);
Assert.That(NumberTheory.IsPrime(641), Is.True);
Assert.That(NumberTheory.IsPrime((long)(int.MaxValue) + 1), Is.False);
foreach (var i in NumberTheory.PrimesLessThan1000)
{
Assert.That(NumberTheory.IsPrime(i), Is.True);
}
}
public void TestIsPrime()
{
Assert.That(NumberTheory.IsPrime(2), Is.True);
Assert.That(NumberTheory.IsPrime(3), Is.True);
Assert.That(NumberTheory.IsPrime(4), Is.False);
Assert.That(NumberTheory.IsPrime(5), Is.True);
Assert.That(NumberTheory.IsPrime(10), Is.False);
Assert.That(NumberTheory.IsPrime(17), Is.True);
Assert.That(NumberTheory.IsPrime(641), Is.True);
//unchecked
//{
// Assert.That(NumberTheory.IsPrime(int.MaxValue + 1), Is.True);
//}
foreach (var i in NumberTheory.PrimesLessThan1000)
{
Assert.That(NumberTheory.IsPrime(i), Is.True);
}
}
public void TestPrintPrimes()
{
int count = 0;
for (int i = 2; i < 104800; i++)
{
if (NumberTheory.IsPrime(i))
{
Console.Write(i + " ");
count++;
if (count % 10 == 0)
{
Console.WriteLine();
}
}
}
Console.WriteLine();
Console.WriteLine(count);
}
