Question

我有一个字符串列表，我想从这个列表中随机选择。挑选字符串时，必须从列表中删除。只有在挑选了所有字符串后，列表才会重新填充。我如何实现这一目标？

Answer 1

首先，制作一个随机数生成器。

Random rand = new Random();

然后，生成一个数字并从列表中删除该项目。我假设你正在使用System.Collections.Generic.List。

int num = Random.Next(list.Count);
list.RemoveAt(num);

Answer 2

你可以非常直接地实现它：

  public static partial class EnumerableExtensions {
    public static IEnumerable<T> RandomItemNoReplacement<T>(this IEnumerable<T> source, 
      Random random) {

      if (null == source)
        throw new ArgumentNullException("source");
      else if (null == random)
        throw new ArgumentNullException("random");

      List<T> buffer = new List<T>(source);

      if (buffer.Count <= 0)
        throw new ArgumentOutOfRangeException("source");

      List<T> urn = new List<T>(buffer.Count);

      while (true) {
        urn.AddRange(buffer);

        while (urn.Any()) {
          int index = random.Next(urn.Count);

          yield return urn[index];

          urn.RemoveAt(index);
        }
      }
    }
  }

然后使用它：

private static Random gen = new Random();    

...

var result = new List<string>() {"A", "B", "C", "D"}
  .RandomItemNoReplacement(gen)
  .Take(10);

// D, C, B, A, C, A, B, D, A, C (seed == 123)  
Console.Write(string.Join(", ", result));

Answer 3

我想，你需要像下一堂课一样思考：

public class RandomlyPickedWord
    {
        public IList<string> SourceWords{ get; set; }

        protected IList<string> Words{ get; set; }

        public RandomlyPickedWord(IList<string> sourceWords)
        {
            SourceWords = sourceWords;
        }

        protected IList<string> RepopulateWords(IList<string> sources)
        {
            Random randomizer = new Random ();
            IList<string> returnedValue;
            returnedValue = new List<string> ();

            for (int i = 0; i != sources.Count; i++)
            {
                returnedValue.Add (sources [randomizer.Next (sources.Count - 1)]);
            }

            return returnedValue;
        }

        public string GetPickedWord()
        {
            Random randomizer = new Random ();
            int curIndex;
            string returnedValue;

            if ((Words == null) || (Words.Any () == false))
            {
                Words = RepopulateWords (SourceWords);
            }

            curIndex = randomizer.Next (Words.Count);
            returnedValue = Words [curIndex];
            Words.RemoveAt (curIndex);

            return returnedValue;
        }
    }

下一步应该使用哪个：

IList<string> source = new List<string> ();
            source.Add ("aaa");
            source.Add ("bbb");
            source.Add ("ccc");
            RandomlyPickedWord rndPickedWord = new RandomlyPickedWord (source);

            for (int i = 0; i != 6; i++)
            {
                Console.WriteLine (rndPickedWord.GetPickedWord ());
            }

从列表中选取一个没有替换C＃的随机字符串

3 个答案: