using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var box = new PrizeBox<string>();

        box.Add("一獎", 20);

        box.Add("二獎", 30);

        box.Add("三獎", 50);

        //抽100次

        foreach (var result in Enumerable.Range(0, 100).Select(x => box.DrawOne()).GroupBy(x => x).Select(x => new

        {

        Count = x.Count(), Prize = x.Key

        }

​

        ))

        {

            Console.WriteLine(result.Prize+" 出現 "+result.Count+" 次");

        }

    }

}

​

public class Prize<T>

{

    public T Item

    {

        get;

        set;

    }

​

    public int Weight

    {

        get;

        set;

    }

​

    public int ? MaxTimes

    {

        get;

        set;

    }

​

    public int DrawedTimes

    {

        get;

        set;

    }

​

    public bool CanDraw

    {

        get;

        set;

    }

​

    public Prize()

    {

        CanDraw = true;

    }

}

​

public class PrizeBox<T> : ICollection<Prize<T>>

{

    static Random random = new Random();

    protected List<Prize<T>> prizeList = new List<Prize<T>>();

    protected Prize<T>[] pool;

    protected int max = 0;

    protected bool boxCalculated = false;

    public int Count

    {

        get

        {

            return prizeList.Count;

        }

    }

​

    public bool IsReadOnly

    {

        get

        {

            return true;

        }

    }

​

    public T DrawOne()

    {

        if (!boxCalculated)

        {

            pool = prizeList.Where(x => x.CanDraw && x.Weight > 0 && (!x.MaxTimes.HasValue || x.DrawedTimes < x.MaxTimes.Value)).ToArray();

            max = pool.Sum(x => x.Weight);

            boxCalculated = true;

        }

​

        if (pool.Length > 0)

        {

            var getLuckNumber = random.Next(1, max);

            foreach (var prize in pool)

            {

                getLuckNumber -= prize.Weight;

                if (getLuckNumber <= 0)

                {

                    prize.DrawedTimes++;

                    if (prize.MaxTimes.HasValue && prize.DrawedTimes >= prize.MaxTimes.Value)

                    {

                        boxCalculated = false;

                    }

​

                    return prize.Item;

                }

            }

        }

        else

        {

            return default (T);

        }

​

        throw new Exception("something wrong");

    }

​

    public void Add(T item, int weight, int ? maxTimes = null)

    {

        Add(new Prize<T>{Item = item, Weight = weight, MaxTimes = maxTimes});

    }

​

    public void Add(Prize<T> item)

    {

        boxCalculated = false;

        prizeList.Add(item);

    }

​

    public void Clear()

    {

        boxCalculated = false;

        prizeList.Clear();

    }

​

    public bool Contains(Prize<T> item)

    {

        return prizeList.Contains(item);

    }

​

    public void CopyTo(Prize<T>[] array, int arrayIndex)

    {

        prizeList.CopyTo(array, arrayIndex);

    }

​

    public bool Remove(Prize<T> item)

    {

        boxCalculated = false;

        return prizeList.Remove(item);

    }

​

    public IEnumerator<Prize<T>> GetEnumerator()

    {

        return prizeList.GetEnumerator();

    }

​

    IEnumerator IEnumerable.GetEnumerator()

    {

        return prizeList.GetEnumerator();

    }

}