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生日悖论说，一个房间里的两个人生日相同的概率是房间里人数（n）的一半以上，大于 23。这个性质并不是真正的悖论，而是许多人对此感到惊讶。设计一个可以通过对随机生成的生日进行一系列实验来测试这个悖论的 C++ 程序，这些实验在 n = 5, 10, 15, 20, 时测试这个悖论。. . , 100。您应该为每个 n 值运行至少 10 次实验，并且它应该为每个 n 输出该 n 的实验次数，这样该测试中的两个人的生日相同。

package birth;
import java.util.Random;

/* Question: 
The birthday paradox says that the probability that two people in a room
will have the same birthday is more than half as long as the number of
people in the room (n), is more than 23. This property is not really a paradox,
but many people find it surprising. Design a C++ program that can
test this paradox by a series of experiments on randomly generated birthdays,
which test this paradox for n =5, 10, 15, 20, . . . , 100. You should run
at least 10 experiments for each value of n and it should output, for each
n, the number of experiments for that n, such that two people in that test
have the same birthday.
*/

public class birth {

public static final int YEAR = 365;

public static void main(String[] args)
{

    int numOfPeople = 5;
    int people = 5;

    //DOB array
    int[] birthday = new int[YEAR];



    //Creates an array that represents 365 days
    for (int i = 0; i < birthday.length; i++)
        birthday[i] = i + 1;

    //Random Number generator
    Random randNum = new Random();

    int iteration = 1;

    //iterates around peopleBirthday array
    while (numOfPeople <= 100)
    {
        System.out.println("Iteration: " + iteration);
        System.out.println();
        //Creates array to holds peoples birthday
        int[] peopleBirthday = new int[numOfPeople];


        //Assigns people DOB to people in the room
        for (int i = 0; i < peopleBirthday.length; i++)
        {
            int day = randNum.nextInt(YEAR + 1);
            peopleBirthday[i] = birthday[day];


        }
        for (int i = 0; i < peopleBirthday.length; i++)
        {   


            //stores value for element before and after
            int person1 = peopleBirthday[i];
            int person2 = i + 1;

            //Checks if people have same birthday
            for (int j = person2; j < peopleBirthday.length; j++)
            {


                //Prints matching Birthday days
                if (person1 == peopleBirthday[j])
                {
                    System.out.println("P1: " + person1 + " P2: " + peopleBirthday[j]);
                    System.out.println("Match!!! \n");

                }
            }
        }


        //Increments the number of people in the room
        numOfPeople += 5;
        iteration++;
    }

    }
}

我收到一个错误：java.lang.ArrayIndexOutOfBoundsException: 365我无法弄清楚我的代码有什么问题

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2 回答 2

2

如果您提供引发异常的确切行号会很好（信息在您获得的错误堆栈跟踪中），但问题很可能发生在这里：

int day = randNum.nextInt(YEAR + 1); // 365 + 1 = 366
peopleBirthday[i] = birthday[day];

Random.nextInt的文档说：

返回：此随机数生成器序列的下一个伪随机、均匀分布的 int 值，介于零（包括）和边界（不包括）之间。

在这种情况下，您使用( )Random.nextInt的值进行调用，这意味着您正在有效地读取 和 之间的一些随机数。如果你确实 get ，那将抛出越界异常，因为你的数组的最大索引是，而不是。366365 + 10365365birthday[day]364365

您可能打算以这种方式读取随机值：

int day = randNum.nextInt(YEAR); // 365 (exclusive)
于 2015-08-29T04:03:56.327 回答
1

Java 中的数组是从零开始的。如果您创建birthday的长度为365，则索引将从0到364。

您需要从此更改此行：

int[] birthday = new int[YEAR];

对此：

int[] birthday = new int[YEAR+1];
于 2015-08-29T03:59:19.103 回答