Find GCD for several numbers at once. Just a common snippet for math problems.

gcd_several_numbers.cs

// gcd for n numbers
static int gcd(int[] numbers)
{
	return numbers.Aggregate(gcd);
}

// gcd for 2
static int gcd(int a, int b)
{
	return b == 0 ? a : gcd(b, a % b);
}

private HashSet<int> FindAllDivisors(List<int> arr)
{
	// Variable to find the gcd 
	// of N numbers 
	int g = arr[0];
	// Set to store all the common divisors 
	HashSet<int> divisors = new HashSet<int>();
	// Finding GCD of the given 
	// N numbers 
	for (int i = 1; i < arr.Count; i++)
	{
		g = gcd(arr[i], g);
	}

	// Finding divisors of the HCF of n numbers 
	for (int i = 1; i * i <= g; i++)
	{
		if (g % i == 0)
		{
			divisors.Add(i);
			if (g / i != i)
				divisors.Add(g / i);
		}
	}

	return divisors;
}