【ProjectEuler】ProjectEuler_002

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本文探讨了斐波那契数列中不超过四百万的偶数值项的总和问题，提供了三种不同的算法实现方法，并对比了它们的运行效率。

// Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
// 
// 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
// 
// By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms.

using System;
using System.Collections.Generic;
using System.Text;
using System.Threading;

namespace projecteule002
{
  class Program
    {
        static void Main(string[] args)
        {
            //F1();
            //F2();
            F3();
        }

        private static void F1()
        {
            Console.WriteLine(new System.Diagnostics.StackTrace().GetFrame(0).GetMethod());
            DateTime timeStart = DateTime.Now;
            int sum = 0;
            int temp;

            for (int i = 0; (temp = Fibonacci(i)) < 4000000; i++)
            {
                if (temp % 2 == 0)
                {
                    sum += temp;
                }
            }
            Console.WriteLine(sum);
            Console.WriteLine("Total Milliseconds is " + DateTime.Now.Subtract(timeStart).TotalMilliseconds + "\n\n");
        }

        private static void F2()
        {
            Console.WriteLine(new System.Diagnostics.StackTrace().GetFrame(0).GetMethod());
            DateTime timeStart = DateTime.Now;

            int sum = 0;
            int temp;

            for (int i = 0; (temp = evenFibonacci(i)) < 4000000; i++)
            {
                sum += temp;
            }
            Console.WriteLine(sum);

            Console.WriteLine("Total Milliseconds is " + DateTime.Now.Subtract(timeStart).TotalMilliseconds + "\n\n");
        }

        private static void F3()
        {
            Console.WriteLine(new System.Diagnostics.StackTrace().GetFrame(0).GetMethod());
            DateTime timeStart = DateTime.Now;
            int sum = 10;
            int f1 = 2;
            int f2 = 8;
            int temp;

            while ((temp = 4 * f2 + f1) < 4000000)
            {
                f1 = f2;
                f2 = temp;
                sum += temp;
            }

            Console.WriteLine(sum);
            Console.WriteLine("Total Milliseconds is " + DateTime.Now.Subtract(timeStart).TotalMilliseconds + "\n\n");
        }

        private static int Fibonacci(int n)
        {
            if (n <= 1)
            {
                return 1;
            }
            else
            {
                return Fibonacci(n - 1) + Fibonacci(n - 2);
            }
        }

        private static int evenFibonacci(int n)
        {
            if (n == 0)
            {
                return 2;
            }
            else if (n == 1)
            {
                return 8;
            }
            else
            {
                return 4 * evenFibonacci(n - 1) + evenFibonacci(n - 2);
            }
        }

    }
}
/*
Void F1()
4613732
Total Milliseconds is 548.0696

Void F2()
4613732
Total Milliseconds is 9.0011

Void F3()
4613732
Total Milliseconds is 5.5007

By GodMoon
*/