C＃中多維數組的隨機化

Question

對於一個小型項目，我正在制作測驗程序。我當前的（相對）代碼如下：

static Random _r = new Random();        
static int Quiz()
{
    string[,] QAndA = {
        {"What is the capital of France", "Paris"},
        {"What is the capital of Spain", "Madrid"},
                ...
        {"What is the captial of Russia", "Moscow"},
        {"What is the capital of Ukraine", "Kiev"},
    };

    for (int i = 0; i < NUM_QUESTIONS; i++)
    {
        int num = _r.Next(QAndA.GetLength(0) / 2);
        Question(QAndA[num, 0], QAndA[num, 1]);
    }
}

現在，明顯的問題是可以重復隨機數，這意味着可以重復問題。

現在，我的老師（是的，這是學校的事情）告訴我尋找改組算法，但是我找不到適合我所使用的多維數組的算法。

我是一個相當新的C＃程序員，但是我有使用c ++的經驗，並且該程序是命令行程序（目前是:)），如果那很重要/有幫助的話

因此，問題是，將多維數組重新排序/改組為隨機順序的最佳方法是什么？

Answer 1

您正在尋找錯誤的問題。 而不是多維數組（因為很少支持，所以很少使用）使用鋸齒數組。

string[][] questions = new[] { 
    new [] {"What is the capital of France", "Paris"}, 
    new [] {"What is the capital of Spain", "Madrid"},
    new [] {"What is the captial of Russia", "Moscow"},
    new [] {"What is the capital of Ukraine", "Kiev"},
};

// use: questions[0][0] (question), questions[0][1] (answer), questions[1][0] (question)...

或（更好）創建一個具有兩個成員的類Question and Answer 。

class QuestionAndAnswer
{
    public string Question { get; protected set; }
    public string Answer { get; protected set; }

    public QuestionAndAnswer(string question, string answer)
    {
        this.Question = question;
        this.Answer = answer;
    }
}

QuestionAndAnswer[] questions = new QuestionAndAnswer[] { 
    new QuestionAndAnswer("What is the capital of France", "Paris"),
    new QuestionAndAnswer("What is the capital of Spain", "Madrid"),
    // ...
};

// use: questions[0].Question, questions[0].Answer...

然后，您可以使用Knuth算法:-)

從那里報價：

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

在C＃中，算法類似於

Random rnd = new Random();

for (int i = questions.Length - 1; i >= 1; i--)
{
    // Random.Next generates numbers between min and max - 1 value, so we have to balance this
    int j = rnd.Next(0, i + 1);

    if (i != j)
    {
        var temp = questions[i];
        questions[i] = questions[j];
        questions[j] = temp;
    }
}

Answer 2

我建議不要使用“多維”數組，如果它不是多維數組。

我的建議：（請在此處實時查看http://ideone.com/NsjfM ）

using System;
using System.Linq;
using System.Collections.Generic;

public class Program
{
    struct QA { public string Q, A; }

    static Random _r = new Random();        
    static int Quiz()
    {
        var QAndA = new QA[] {
            new QA { Q = "What is the capital of France"  , A = "Paris"}, 
            new QA { Q = "What is the capital of Spain"   , A = "Madrid"}, 
            //  ...
            new QA { Q = "What is the captial of Russia"  , A = "Moscow"}, 
            new QA { Q = "What is the capital of Ukraine" , A = "Kiev"}, 
        };

        foreach (var qa in QAndA.OrderBy(i => _r.Next()))
        {
            Question(qa.Q, qa.A);
        }

        return 0;
    }

    public static void Main(string[] args)
    {
        int n = Quiz();
    }

    private static void Question(string q, string a)
    {
        Console.WriteLine("Q. {0}", q);
        Console.WriteLine("A. {0}", a);
    }

}

Answer 3

maybe better (without shouffling, without repeatable questions):       



class QuizQuestion
{
public string Question {get; set;}
public string Answer {get; set;}
}

static Random _r = new Random();        
        static int Quiz()
        {
            QuizQuestion[] QAndA = new QuizQuestion[] {
                new QuizQuestion() {Question = "What is the capital of France", Answer = "Paris"},
                new QuizQuestion() {Question = "What is the capital of Spain", Answer ="Madrid"},
                        ...
                new QuizQuestion() {Question = "What is the captial of Russia", Answer ="Moscow"},
                new QuizQuestion() {Question = "What is the capital of Ukraine", Answer ="Kiev"},
            };

            var questions = QAndQ.ToList();
            for (int i = 0; i < NUM_QUESTIONS; i++)
            {
                int num = _r.Next(questions.Length / 2);
                Question(questions[num].Question, questions[num].Answer);
                questions.Remove(questions[num]);
            }
        }

Answer 4

實際上，您正在重新排序一個二元數組，因為您不應該整理答案;）最簡單的算法可能是：

   foreach array index
      switch with random index in array

Answer 5

不需要重新排列數組的方法，並且如果您只需要選擇幾個問題，則該方法會更快，該方法是將選擇的問題存儲在一組中。

繼續生成隨機數，並在集合大小正確后將其添加到集合的索引處。

您的循環將類似於：

var questions = new HashSet<Question>();
while (questions.Count < numberOfQuestionsRequired)
{
  questions.Add(questionArray[_r.Next()])
}

HashSet<>.Count和HashSet<>.Add()均為O（1），因此限制因素將是碰撞了多少個隨機數。