随机化列表<string>没有重复 [英] Randomize List&lt;string&gt; without duplicates

问题描述

我有一个

List<string> notizen = new List<string>();

我想从中随机选择一个条目，但在显示通知的所有条目之前不应重复此条目.

I want to choose a random entry from it but this entry should not be repeated until all entries of notizen have been shown.

应用程序如下所示:

字符串在屏幕上，您点击它，屏幕上就会出现另一个文本.我想随机浏览通知列表，不要重复输入，直到显示所有条目，然后从一个新的随机版本的通知开始.

String is on the screen, you tap on it, another text is on the screen. I want to randomly go through the notizen list without having double entries until all entries have been shown, then it starts with a new randomized version of notizen.

notizen 本身可以随机化，不需要临时列表.但我发现 LINQ 在 monodroid 中不存在.

notizen could be randomized itself, no temporary list necessary. But I found LINQ to not exist in monodroid.

推荐答案

您可以使用 O(n) 中的nofollow">Fisher-Yates 算法；一旦您的迭代器等于 n，则执行第二次 shuffle，依此类推.

You can shuffle your List using Fisher–Yates algorithm in O(n); once your iterator equals n, perform a second shuffle and so on.

它的伪代码，如维基百科所示，是:

The pseudocode for it, as presented in wikipedia, is :

To shuffle an array a of n elements (indices 0..n-1):
  for i from n − 1 downto 1 do
   j ← random integer with 0 ≤ j ≤ i
   exchange a[j] and a[i]

您甚至可以为此编写扩展方法，例如:

You could even write an extension method for that, something like :

    public static Random rand = new Random();

    public static List<T> Shuffle<T>(this List<T> original)
    {
        List<T> lst = new List<T>(original);
        for (int i = lst.Count - 1; i >= 1; i--)
        {
            int j = rand.Next(0, i + 1);
            T tmp = lst[j];
            lst[j] = lst[i];
            lst[i] = tmp;
        }
        return lst;
    }

以便您可以使用

var shuffled = notizen.Shuffle();

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