second-largest.cs

public static class Math
{
	public static T SecondLargest<T>(IEnumerable<T> inputs) where T : IComparable<T>
	{
		// Null checks skipped for brevity
		var (largest, second) = (default(T), default(T));
		foreach (var input in inputs)
		{
			if (input.CompareTo(largest) > 0)
			{
				(largest, second) = (input, largest);
			}
			else if (input.CompareTo(second) > 0)
			{
				second = input;
			}
		}

		return second;
	}
}