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[转载]关于网站抽奖活动算法的尝试  

2013-01-15 14:30:49|  分类: 算法 |  标签: |举报 |字号 订阅

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遇到一个需求,某网站为了吸引人气,要开展抽奖活动,需求主要有以下几点:

1.共分一、二、三等奖,要控制一等奖尽量不要一开始就抽掉;

2.活动长期开展,持续时间一周左右,要使每天的各奖项概率趋于一致;

3.为保证每天活动参与人数,要确保在限定人数附近抽出所有奖项;

 

基于以上几点,做出如下设计:

1.首先要输入天预估总人数,并将奖品平均分到每天,得到各奖项的日均奖品数(可能为小数);

2.计算各奖项的抽奖概率,日均奖品数/日抽奖总人数;

3.产生一个随机双精度数,若小于等于概率则视为抽中;

4.一次抽奖开始时,先抽取三等奖,若中奖则提示,若不中奖则继续抽取二等奖,若再不中奖则抽取一等奖;

5.每次抽奖过后,若抽中奖品则预估总人数-1,并且所有概率重新计算,并应用于下一轮抽奖;

6.若总人数小于一个限定阀值,则停止概率变化,用此概率完成全部抽奖;

7.当天奖品总数小于1时,抽奖结束,小数部分流入后一天继续抽奖。

 

大概思路如上,设计较为简单,没有技术含量,会有的问题就是理论上后一天一开始抽奖的概率会偏高一些,也曾想用某些数学公式定理来解决,但因为对概率论不了解,不了了之。

顺手贴上第一天所有抽奖的代码,希望感兴趣的朋友多给些宝贵意见!

 

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

namespace Lottery
{
    class Program
    {
        private static string InputString;//输入字符串
        private static int LevelCount;//
        private static int DayNum;//
        private static int DayUserNum;//
        private static int[] arrPrizeNum;//
        private static double[] AvgPrizeNum;
        private static double TotalPrizeNum;
        private static double[] ArProbability;


        public static Random rand = new Random((int)DateTime.Now.Ticks);

        static void Main(string[] args)
        {
            ShowInfo();
            GetInputNum("请输入奖项总数:", ref LevelCount);
            arrPrizeNum = new int[LevelCount];
            InputPrizeNum();
            GetInputNum("请输入预计抽奖天数:", ref DayNum);
            GetInputNum("请输入第一天预估总人数:", ref DayUserNum);
            BeginLottery();
        }

        private static void ShowInfo()
        {
            Console.WriteLine("欢迎使用随机抽奖系统!");
        }

        private static void InputPrizeNum()
        {
            for (int i = 0; i < LevelCount; i++)
            {
                GetInputNum("请输入 " + (i + 1) + " 等奖奖品数目:", ref arrPrizeNum[i]);
            }
        }

        private static void GetInputNum(string words, ref int target)
        {
            while (true)
            {
                Console.WriteLine(words);
                InputString = Console.ReadLine();
                int temp = SafeParse(InputString);
                if (temp != -1)
                {
                    target = temp;
                    break;
                }
                else
                {
                    Console.WriteLine("您的输入有误,请输入整型数字!");
                    continue;
                }
            }
        }

        private static int SafeParse(object obj)
        {
            int temp;
            if (!int.TryParse(obj.ToString(), out temp))
            {
                temp = -1;
            }
            return temp;
        }

        private static void BeginLottery()
        {
            AvgPrizeNum = new double[LevelCount];
            ArProbability = new double[LevelCount];
            TotalPrizeNum = 0;

            for (int i = 0; i < LevelCount; i++)
            {
                TotalPrizeNum += arrPrizeNum[i];
            }
            for (int i = 0; i < LevelCount; i++)
            {
                AvgPrizeNum[i] = (double)arrPrizeNum[i] / (double)DayNum;
            }
            for (int i = 0; i < LevelCount; i++)
            {
                ArProbability[i] = (double)AvgPrizeNum[i] / (double)DayUserNum;
            }

            for (int j = 0; j < 10000; j++)
            {
                double x = rand.NextDouble();
                for (int i = LevelCount - 1; i >= 0; i--)
                {
                    if (x < ArProbability[i])
                    {
                        if (AvgPrizeNum[i] > 1)
                        {
                            AvgPrizeNum[i]--;
                            Console.WriteLine("恭喜您,抽到了" + (i + 1) + "等奖!");
                            LotteryOnit();
                            //Console.ReadLine();
                            break;
                        }
                        else
                        {
                            continue;
                        }
                    }
                    else
                    {
                        Console.WriteLine("很遗憾,欢迎下次再来!" + DayUserNum);
                        x = rand.NextDouble();
                        LotteryOnit();
                        continue;
                    }
                }
                if (DayUserNum > TotalPrizeNum / DayNum)
                {
                    DayUserNum--;
                }
                for (int i = 0; i < AvgPrizeNum.Length; i++)
                {
                    if (AvgPrizeNum[i] >1)
                    {
                        break;
                    }
                    if (i == AvgPrizeNum.Length - 1)
                    {
                        Console.WriteLine("共" + j + "位用户参与," + "奖已抽完!");
                        Console.ReadLine();
                    }
                }
                Console.WriteLine();
            }
            Console.ReadLine();
        }

        private static void LotteryOnit()
        {
            for (int i = 0; i < LevelCount; i++)
            {
                ArProbability[i] = (double)AvgPrizeNum[i] / (double)DayUserNum;
                Console.WriteLine("第"+(i+1)+"等奖的概率变为:"+ArProbability[i].ToString());
                Console.WriteLine(AvgPrizeNum[i] + "    " + DayUserNum);
            }
        }
    }
}
转载地址:http://blog.csdn.net/suneboy/article/details/6176444

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