概率计数中的Java输出

考虑到数学输出和程序给出的结果之间的差异，我遇到了一个问题

我想以1/6的概率计算两次获得相同数字的概率，这应该是

1/6*1/6=36

。然而，我得到的答案是1/42-43。怎么了

int guess = (int) (Math.random() * 6);
int real = (int) (Math.random() * 6);
int countTot = 0;
int countReal = 0;
int countGen = 0;

while (true) {
    if (countReal == 2) {
        countGen++;
        countReal = 0;
        if (countGen == 1000000) {
            System.out.println("Probability: 1 in " + countTot/countGen);
            System.exit(0);
        }
    }
    if (guess == real) {
        countReal++;
        countTot++;
    } else {
        countReal = 0;
        countTot++;
    }
    guess = (int) (Math.random() * 6);
    real = (int) (Math.random() * 6);
}

---

假设我做了1000000次（

countGen

），并取结果的平均值。提前感谢。

运行以下代码：

int n = 1_000_000;
int count = 0;
Random rnd = new Random();

for (int i = 0; i < n; i++) {
    int a = rnd.nextInt(6);
    int b = rnd.nextInt(6);
    int c = rnd.nextInt(6);
    int d = rnd.nextInt(6);

    if (a == b && c == d) {
        count++;
    }
}

System.out.println(count + " / " + n);
System.out.println("Or about 1 in " + (n * 1.0 / count));

---

你算错了。您正在将抛出次数（countTot）与成功的双重比较次数进行比较。你应该得到它1/72。但你们并没有得到它，因为若第一对不匹配，若提前退出

下面的代码给出了正确的答案。这不是很好，我会重新命名大多数东西，但我想保持它尽可能类似于原来的

int guess = (int) (Math.random() * 6);
    int real = (int) (Math.random() * 6);
    int countTot = 0;
    int countReal = 0;
    int countGen = 0;

    while (true) {
        if (countReal == 2) {
            countGen++;
            countReal = 0;
            if (countGen == 1000000) {
                System.out.println("Probability: 1 in " + (countTot/2)/countGen);
                System.exit(0);
            }
        }
        if (guess == real) {
            countReal++;
            countTot++;
        } else {
            countTot++;
            if ( countReal == 0 ) {
                countTot++;
            }
            countReal = 0;
        }
        guess = (int) (Math.random() * 6);
        real = (int) (Math.random() * 6);
    }

---

在不允许重叠的情况下计算连续匹配对的数量。如果你得到一个由3个相等的随机数组成的序列，你应该数到2对，但你只能数到一对。不允许重叠意味着一对取决于它之前的内容。为了能够增加概率，你必须保证事件是独立的。

而且这个算法也比OP的算法更清晰。谢谢你的帮助，我现在明白了！谢谢你的帮助，我现在明白了！

int guess = (int) (Math.random() * 6);
    int real = (int) (Math.random() * 6);
    int countTot = 0;
    int countReal = 0;
    int countGen = 0;

    while (true) {
        if (countReal == 2) {
            countGen++;
            countReal = 0;
            if (countGen == 1000000) {
                System.out.println("Probability: 1 in " + (countTot/2)/countGen);
                System.exit(0);
            }
        }
        if (guess == real) {
            countReal++;
            countTot++;
        } else {
            countTot++;
            if ( countReal == 0 ) {
                countTot++;
            }
            countReal = 0;
        }
        guess = (int) (Math.random() * 6);
        real = (int) (Math.random() * 6);
    }