c#斐波那契数列(Fibonacci)(递归,非递归)实现代码

//main

using system;
using system.collections.generic;
using system.linq;
using system.text;

namespace fibonacci
{
    class program
    {
        static void main(string[] args)
        {
            console.writeline("would you like to know which fibonacci numbers：");
            int number = convert.toint32(console.readline());
            //
            function obj = new function();
            console.writeline();
            console.write("the {0} fibonacci number is：{1}", number, obj.fibonacci(number));
            //
            console.writeline();
            function obj2 = new function(number);
            console.write("the {0} fibonacci number is：{1}", number, obj2.bottomupnotrecursion(number));
            //
            console.writeline();
            console.write("the {0} fibonacci number is：{1}", number, obj2.topdownrecursion(number));
            console.readkey();

        }
    }
}

//class

using system;
using system.collections.generic;
using system.linq;
using system.text;

namespace fibonacci
{
    class function
    {
        private int[] array;

        public function()
        {

        }

        /// <summary>
        /// function
        /// </summary>
        /// <param name="length"></param>
        public function(int length)
        {
            if (length > 0)
            {
                array = new int[length + 1];
                array[0] = 1;
                array[1] = 1;
            }
            if (length == 0)
            {
                array = new int[1];
                array[0] = 1;
            }
        }

        /// <summary>
        /// fibonacci数列定义为：
        ///             无穷数列1，1，2，3，5，8，13，21，34，55，……
        ///        ┌ 1             n=0    
        ///   f(n)=│ 1             n=1
        ///        └ f(n-1)+f(n-2) n>1
        /// </summary>
        /// <param name="number">第几个斐波那契数</param>
        /// <returns></returns>
        public int fibonacci(int number)
        {
            if (number <= 1)
            {
                return 1;
            }
            else
            {
                return fibonacci(number - 1) + fibonacci(number - 2);
            }
        }

        /// <summary>
        /// 动态规划思想：
        ///     1.自底向上非递归算法
        /// </summary>
        /// <param name="number"></param>
        /// <returns></returns>
        public int bottomupnotrecursion(int number)
        {
            int copynumber = 0;
            if (number < 2)
            {
                copynumber = 1;
            }
            else
            {
                int one = array[0];
                int two = array[1];

                for (int i = 2; i < array.length; i++)
                {
                    array[i] = one + two;
                    one = two;
                    two = array[i];
                    copynumber = array[i];
                }
            }

            return copynumber;
        }

        /// <summary>
        ///     2.自顶向下递归算法
        /// </summary>
        /// <param name="number"></param>
        /// <returns></returns>
        public int topdownrecursion(int number)
        {
            if (number <= 2)
            {
                if (number == 0)
                    return array[0];
                if (number == 1)
                    return array[1];
                if (number == 2)
                    return array[2] = array[0] + array[1];
            }
            else
            {
                //递归只是一个“牵引线”，目的是为了让数组储存值。
                topdownrecursion(number - 1);
                array[number] = array[number - 1] + array[number - 2];
            }
            return array[number];
        }
    }
}

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