using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        const int Iterations = 100000;

        var uqBag = new WeightedRandomBag<string>()

        {

            ("UwU",1),

            ("...",200),

            ("DeadInside",20),

        };

        var resultDictionary = uqBag.ToDictionary(item => item.Item, item => 0);

        for (var i = 0 ; i < Iterations ; i++)

        {

            var randomItem = uqBag.GetRandomItem();

            resultDictionary[randomItem]++;

        }

        Console.WriteLine(string.Join("\n", resultDictionary.Select(p => $"{p.Key}, {p.Value}")));

    }

}

​

    /// <summary>

    /// A collection of items that can be randomly selected

    /// from using weighted ratio probability

    /// </summary>

    /// <typeparam name="T"></typeparam>

    public class WeightedRandomBag<T> :IEnumerable<(T Item, double AccumulatedWeight)>

    {

        private Random random = new Random();

        private List<(T Item, double AccumulatedWeight)> _items = new List<(T, double)>();

        private double accumulatedWeight;

​

        public void Add((T Item, double Weight) weightedItem)

        {

            accumulatedWeight += weightedItem.Weight;

            _items.Add((weightedItem.Item, accumulatedWeight));

        }

​

        public void Add(IEnumerable<(T Item, double Weight)> itemWeights)

        {

            _items.AddRange(itemWeights);

        }

​

        /// <summary>

        /// Gets a random object in the collection based

        /// on the weighted ratios

        /// </summary>

        /// <returns></returns>

        public T GetRandomItem()

        {

            var randomWeight = random.NextDouble() * accumulatedWeight;

            return _items.First(item => item.AccumulatedWeight >= randomWeight).Item;

        }

​

        public IEnumerator<(T Item, double AccumulatedWeight)> GetEnumerator()

        {

            return _items.GetEnumerator();

        }

​

        IEnumerator IEnumerable.GetEnumerator()

        {

            return _items.GetEnumerator();

        }

    }

​