Fibonacci数列

非递归写法

static int FibonacciNumber(int n)
        {
            int a = 0;
            int b = 1;
            int tmp;

            for (int i = 0; i < n; i++)
            {
                tmp = a;
                a = b;
                b += tmp;
            }

            return a;
        }

递归写法

 static void Main(string[] args)
        {
            var genaerator = new FibonacciGenerator();
            foreach (var digit in genaerator.Generate(15))
            {
                Console.WriteLine(digit);
            }
        }

 public class FibonacciGenerator
    {
        private Dictionary<int, int> _cache = new Dictionary<int, int>();
        private int Fib(int n) => n < 2 ? n : (FibValue(n - 1) + FibValue(n - 2));

        private int FibValue(int n)
        {
            if (!_cache.ContainsKey(n))
            {
                _cache.Add(n, Fib(n));
            }
            return _cache[n];
        }

        public IEnumerable<int> Generate(int n)
        {
            for (int i = 0; i < n; i++)
            {
                yield return FibValue(i);
            }
        }
    }