Задача Ступеньки

Stairs.cs

using System;
					
public class Program
{
	private static long GetAllCombinations(int n)
	{
		long[] memoArr = new long[n + 1];
		return GetCombinationCount(0, n, ref memoArr);
	}	
	
	private static long GetCombinationCount(int index, int n, ref long[] memoArr)
	{
		if (index > n)
		{
			return 0;
		}
		if (index == n)
		{
			return 1;
		}
		if (memoArr[index] > 0)
		{
			return memoArr[index];
		}
		memoArr[index] = GetCombinationCount(index + 1, n, ref memoArr) + GetCombinationCount(index + 2, n, ref memoArr);
		return memoArr[index];
	}
	
	private static long GetFibonacciNumber(long n)
	{
		if (n == 1)
		{
			return 1;
		}
		long f1 = 1;
		long f2 = 2;
		for (int i = 3; i <= n; i++)
		{
			long fi = f1 + f2;
			f1 = f2;
			f2 = fi;
		}
		return f2;
	}
	
	public static void Main()
	{
		Console.WriteLine("UniLecs");
		
		Console.WriteLine(string.Format("Answer = {0}", GetAllCombinations(3))); // 3
		Console.WriteLine(string.Format("Answer = {0}", GetFibonacciNumber(3))); // 3
	}
}