javascript - 在JavaScript中生成特定范围内的随机整数？(Generating random whole numbers in JavaScript in a specific range?)

Question

如何可以生成两个指定的变量之间的随机整数在JavaScript中，例如x = 4和y = 8将输出任何的4, 5, 6, 7, 8 ？

  ask by zacharyliu translate from so

Answer 1

There are some examples on the Mozilla Developer Network page:

(Mozilla开发人员网络页面上有一些示例：)

/**
 * Returns a random number between min (inclusive) and max (exclusive)
 */
function getRandomArbitrary(min, max) {
    return Math.random() * (max - min) + min;
}

/**
 * Returns a random integer between min (inclusive) and max (inclusive).
 * The value is no lower than min (or the next integer greater than min
 * if min isn't an integer) and no greater than max (or the next integer
 * lower than max if max isn't an integer).
 * Using Math.round() will give you a non-uniform distribution!
 */
function getRandomInt(min, max) {
    min = Math.ceil(min);
    max = Math.floor(max);
    return Math.floor(Math.random() * (max - min + 1)) + min;
}

---

Here's the logic behind it.

(这是背后的逻辑。)

It's a simple rule of three:

(这是三个简单的规则：)

Math.random() returns a Number between 0 (inclusive) and 1 (exclusive).

(Math.random()返回一个介于0（含）和1（ Math.random()之间的Number 。)

So we have an interval like this:

(所以我们有一个这样的间隔：)

[0 .................................... 1)

Now, we'd like a number between min (inclusive) and max (exclusive):

(现在，我们想要一个介于min （含）和max （不含）之间的数字：)

[0 .................................... 1)
[min .................................. max)

We can use the Math.random to get the correspondent in the [min, max) interval.

(我们可以使用Math.random在[min，max）间隔中获取对应的对象。)

But, first we should factor a little bit the problem by subtracting min from the second interval:

(但是，首先我们应该通过从第二个间隔中减去min来解决这个问题：)

[0 .................................... 1)
[min - min ............................ max - min)

This gives:

(这给出：)

[0 .................................... 1)
[0 .................................... max - min)

We may now apply Math.random and then calculate the correspondent.

(现在我们可以应用Math.random ，然后计算对应的对象。)

Let's choose a random number:

(让我们选择一个随机数：)

                Math.random()
                    |
[0 .................................... 1)
[0 .................................... max - min)
                    |
                    x (what we need)

So, in order to find x , we would do:

(因此，为了找到x ，我们要做：)

x = Math.random() * (max - min);

Don't forget to add min back, so that we get a number in the [min, max) interval:

(别忘了加min ，这样我们就可以在[min，max）间隔中得到一个数字：)

x = Math.random() * (max - min) + min;

That was the first function from MDN.

(这是MDN的第一个功能。)

The second one, returns an integer between min and max , both inclusive.

(第二个，返回介于min和max之间（包括两个端点）的整数。)

Now for getting integers, you could use round , ceil or floor .

(现在要获取整数，可以使用round ， ceil或floor 。)

You could use Math.round(Math.random() * (max - min)) + min , this however gives a non-even distribution.

(您可以使用Math.round(Math.random() * (max - min)) + min ，但这会产生不均匀的分布。)

Both, min and max only have approximately half the chance to roll:

(min和max滚动率只有大约一半：)

min...min+0.5...min+1...min+1.5   ...    max-0.5....max
└───┬───┘└────────┬───────┘└───── ... ─────┘└───┬──┘   ← Math.round()
   min          min+1                          max

With max excluded from the interval, it has an even less chance to roll than min .

(如果从间隔中排除了max ，则滚动的机会比min还要少。)

With Math.floor(Math.random() * (max - min +1)) + min you have a perfectly even distribution.

(使用Math.floor(Math.random() * (max - min +1)) + min您可以获得完美的均匀分布。)

min.... min+1... min+2 ... max-1... max.... max+1 (is excluded from interval)
|        |        |         |        |        |
└───┬───┘└───┬───┘└─── ... ┘└───┬───┘└───┬───┘   ← Math.floor()
   min     min+1               max-1    max

You can't use ceil() and -1 in that equation because max now had a slightly less chance to roll, but you can roll the (unwanted) min-1 result too.

(您不能在该方程式中使用ceil()和-1 ，因为max现在滚动的机会略少，但是您也可以滚动（不需要的） min-1结果。)