public void P0012(int numDivisors, long expected)
{
var i = 0;
var triangleNumber = 0L;
var primes = new PrimeNumberGenerator();
while (true)
{
triangleNumber = Functions.TriangleNumber(++i);
var numDivisorsSeen = Functions.NumDivisors(triangleNumber, primes);
if (numDivisorsSeen > numDivisors)
{
break;
}
}
Assert.Equal(expected, triangleNumber);
}
public static Dictionary <long, int> Factor(long i, PrimeNumberGenerator primes)
{
var result = new Dictionary <long, int>();
var primesList = primes.Primes().TakeWhile(x => x <= i).ToList();
var primesCount = primesList.Count();
long p = 0;
for (int j = 0; j < primesCount; j++)
{
p = primesList[j];
if (i % p == 0)
{
result[p] = 0;
var i2 = i;
while (i2 % p == 0)
{
result[p]++;
i2 /= p;
}
}
}
return(result);
}
public static int NumDivisors(long i, PrimeNumberGenerator primes) => Factor(i, primes).Values.Product(x => x + 1);
