求用1，2，5这三个数不同个数组合的和为100的组合个数

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ExchangeDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            int number1, number2;
            Console.WriteLine("求用1，2，5这三个数不同个数组合的和为100的组合个数");
            number1 = SimpleSolution();
            Console.WriteLine("算法一组合数：" + number1 + "");
            number2 = Optimize();
            Console.WriteLine("算法二组合数：" + number2 + "\r\n");

            int nu1 = 0;
            int nu2 = 0;
            int nu5 = 0;
            int count = 0;
            for (nu5 = 0; nu5 < 21; nu5++)
            {
                for (nu2 = 0; nu2 < 51; nu2++)
                {
                    for (nu1 = 0; nu1 < 101; nu1++)
                    {
                        if (nu1 + nu2*2 + nu5*5 == 100)
                        {
                            if (nu1 != 0)
                            {
                                Console.Write("" + nu1 + "*1");
                            }
                            if (nu2 != 0 && nu5 != 0)
                            {
                                Console.Write("+" + nu2 + "*2+" + nu5 + "*5");
                            }
                            else if (nu2 != 0 && nu5 == 0)
                            {
                                Console.Write("+" + nu2 + "*2");
                            }
                            else if (nu2 == 0 && nu5 != 0)
                            {
                                Console.Write("+" + nu5 + "*5");
                            }
                            Console.WriteLine("=100\r\n");
                            count++;
                        }
                    }
                }
            }
            Console.WriteLine("总的组合数为" + count + "");
            Console.Read();

        }
     public static int SimpleSolution()
        {
        int number=0;
        for(int i=0;i<=100;i++)
           for(int j=0;j<=50;j++)
            for(int k=0;k<=20;k++)
            {
             if(i+2*j+5*k==100)
              number++;
            }
        return number;
        }

       public static int Optimize()
        {
           //组合总数为100以内的偶数+95以内的奇数+90以内的偶数+...+5以内的奇数+1
            int number = 0;
            for (int m = 0; m <= 100; m += 5)
            {
                number += (m + 2) / 2;
                // 某个偶数m以内的偶数个数（包括0）可以表示为m/2+1=(m+2)/2
                //某个奇数m以内的奇数个数也可以表示为(m+2)/2
            }
            return number;
        }
    }
}