我试图生成一个随机的3或4位数字

Question

我试图在Java中生成一个随机的3位或4位数字，而不使用循环、数组或方法（生成随机数的内置数学随机方法除外），只是一些基本的东西，比如if语句。

我试过了

（int）（Math.random（）*9899100）；

但它只返回4位数的模糊数字。我的意思是，任何数字都不应该重复。像232、7277、889、191这样的数字是不允许的。但像1234、3456、8976、435这样的数字是不同的，是允许的

Answer 1

下面的代码不会公平地生成数字，但可以生成任何4位数字，3位数字中不会包含0。

// first digit between 0 and 9, if it's 0 we will have a 3 digit number
int first = (int)(Math.random() * 10);  

int second = (int)(Math.random() * 10);
// if it's the same as the first add one to it, use modulo to wrap around
if (first == second)
    second = (second + 1) % 10;

// the same as with second digit just with more checks
int third = (int)(Math.random() * 10);
if (third == first || third == second)
    third = (third + 1) % 10;
// if it's still the same, add one once more, after doing it a second time new digit is guaranteed 
if (third == first || third == second)
    third = (third + 1) % 10;

// the same as with second digit just with more checks
int fourth = (int)(Math.random() * 10);
if (fourth == first || fourth == second || fourth == third)
    fourth = (fourth + 1) % 10;
if (fourth == first || fourth == second || fourth == third)
    fourth = (fourth + 1) % 10;
if (fourth == first || fourth == second || fourth == third)
    fourth = (fourth + 1) % 10;

System.out.println(1000 * first + 100 * second + 10 * third + fourth);

您可以将新数字添加到自身，而不是添加一个以获得更均匀的分布，这需要处理一些角落情况。