C#中多维数组的随机化

Question

对于一个迷你项目，我正在制作一个测验程序 我当前（相关）代码如下：

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]);
    }
}

现在，这样做的明显问题是随机数可以重复，这意味着问题可以重复。

现在，我的老师（是的，这是学校的事情）告诉我要寻找洗牌算法，但我没有找到像我用过的那样适用于多维数组的任何算法。

我是一个相当新的 c# 程序员，但我有 c++ 经验 并且该程序是一个命令行程序（目前:)），如果这很重要/有帮助

那么，问题是，将多维数组重新排序/改组为随机顺序的最佳方法是什么？

Answer 1

您正在寻找错误的问题。使用交错数组代替多维数组（很少使用，因为几乎不支持）。

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)...

或者（更好）创建一个包含两个成员的类，Question 和 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:-)

从那里引用：

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，算法类似于

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

我建议不使用“多维”数组，如果它是......不是多维数组。

我的建议：（看它住在这里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

实际上你正在重新排列一个维度数组，因为你不应该打乱答案；）最简单的算法可能是：

   foreach array index
      switch with random index in array

Answer 5

一种不需要您重新排列数组并且如果您只需要选择几个问题会更快的方法是将您选择的问题存储在一个集合中。

继续生成随机数并将该索引处的问题添加到集合中，一旦集合的大小正确，就返回它。

您的循环将类似于：

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

HashSet<>.Count 和 HashSet<>.Add() 都是 O(1)，所以限制因素是有多少随机数发生冲突。