我正在尝试制作代表生日悖论的程序。我理解这个悖论,我很确定我的代码是错的,但我不确定我哪里出错了。我查看了相关帖子,但我没有发现任何有用的信息。我年轻的时候写了代码,很抱歉,如果有点乱。我知道还有其他方法可以做到这一点,我理解为什么这些工作。我只是想知道为什么我的代码不起作用。谢谢!
编辑:对不起,已经很晚了。忘了提出我的实际问题。我运行它是如何的,并期望得到约50.5%,这是理论值。但是,相反,我得到了大约21.1%。public class Main {
static int trialsSucceeded = 0; // Stores number of successful trials
static final int TRIALS = 1000000; // 1,000,000 is a good number :) Biggest I've tried: 2,147,483,647, which is Integer.MAX_VALUE
static int numberOfPeople = 23; // The 'n' value for the birthday paradox
public static void main(String[] args) {
ArrayList<Integer> birthdays = new ArrayList<Integer>(); // Stores people's birthdays
// Runs until desired trials are completed
for (int trialNumber = 0; trialNumber < TRIALS; trialNumber++) {
// Provides progress updates to user
if (trialNumber % 1000 == 0)
System.out.printf("%.1f%% complete\n", (double) trialNumber * 100 / TRIALS);
// Populates the birthdays array
for (int personNumber = 0; personNumber < numberOfPeople; personNumber++) {
birthdays.add(getRandInt(1, 365));
}
// Used later to see if current trial should end
int prevTrialsSucceeded = trialsSucceeded;
// Checks each person's birthday against everyone else's
for (int i = 0; i < birthdays.size(); i++) {
for (int j = i + 1; j < birthdays.size(); j++) {
// If birthdays match, marks trial as a success jumps to next trail
if ((birthdays.get(i) == birthdays.get(j))) {
trialsSucceeded += 1;
break;
}
}
// Jumps to next trial if this one has already succeeded
if (prevTrialsSucceeded != trialsSucceeded) {
break;
}
}
// Clears list of birthdays to get ready for next trial
birthdays.clear();
}
// Tells user ratio of successful trials to total trials
System.out.println(((double) trialsSucceeded / TRIALS * 100) + "% of trials succeeded");
}
private static int getRandInt(int lowerBound, int upperBound) {
// Returns random integer between lowerBound and upperBound
Random random = new Random();
return random.nextInt(upperBound - lowerBound + 1) + lowerBound;
}
}
答案 0 :(得分:2)
根本问题是这一行:
if ((birthdays.get(i) == birthdays.get(j))) {
这是比较Integer
个对象以确保身份相同。你需要做的是比较价值平等:
if ((birthdays.get(i).equals(birthdays.get(j)))) {
这应该会给你正确的结果,略高于50%。
答案 1 :(得分:1)
正如其他人的想法一样,你的问题根源于比较参考文献......但即使在解决这个问题时,这里的解决方案既不高效也不容易掌握。
有一种更简单的方法可以检查:只需使用Set来存储随机数生日而不是列表。但在添加下一个数字之前,您可以使用Set.contains()来检查该数字是否已在该集合中。如果是这样,你找到了一场比赛......你可以在那里停下来!