如何递归地嵌套for循环？ [英] How to make n nested for loops recursively?

问题描述

我有一个必须执行以下操作的方法：

I have a method that must do the following:

for (int a01 = 1; a01 <= 25; a01++) {
    for (int a02 = a01 + 1; a02 <= 25; a02++) {
        for (int a03 = a02 + 1; a03 <= 25; a03++) {
            ...
            System.out.println(a01 + "," + a02 + "," + ... + "," + a015);
        }
    }
}

我想指定嵌套的数量（在上面的例子中，我想要15嵌套）。
有没有办法在这里使用递归编程？

I'd like to specify the number of nested for's (in the case above, I want 15 nested for's). Is there a way to use recursive programming here?

推荐答案

是的。这可以通过递归编程来执行。

Yes. This can be performed by recursive programming.

我假设您不喜欢在源代码中嵌套这些嵌套 - 就像在您的示例中一样，因为这是非常难看的编程 - 就像评论员解释一样。

I assume you do not like to WRITE DOWN these nested for's in source code - as in your example, because this is really ugly programming - like the commentors explain.

以下（伪类Java）代码说明了这一点。我假设嵌套的固定深度。那么你实际上喜欢循环一个维度深度的整数向量。

The following (pseudo Java-like) code illustrates it. I assume a fixed depth for the nesting. Then you actually like to loop over an integer vector of dimension depth.

int[] length = new int[depth];
int[] counters = new int[depth];

数组计数器必须初始化为0（ Arrays.fill（counter，0））。必须将数组 length 初始化为相应for循环的迭代次数。

The array counters has to be initialised to 0 (Arrays.fill(counters,0)). The array length has to be initialised to the number of iterations for the respective for loop.

我假设你喜欢在内循环中执行某个操作。我将这个
称为 performOperation（int [] counter）;
- 它取决于多维计数器，即外部的计数器。

I assume that you like to perform a certain operation within the inner loop. I will call this performOperation(int[] counters); - it depends on the multi-dimensional counter, i.e. the counters of the outer for's.

然后你可以通过调用

nestedLoopOperation(counters, length, 0);

其中

void nestedLoopOperation(int[] counters, int[] length, int level) {
    if(level == counters.length) performOperation(counters);
    else {
        for (counters[level] = 0; counters[level] < length[level]; counters[level]++) {
            nestedLoopOperation(counters, length, level + 1);
        }
    }
}

在你的情况下你的系统。 out.println（）将

In your case your System.out.println() would be

performOperation(int[] counters) {
    String counterAsString = "";
    for (int level = 0; level < counters.length; level++) {
        counterAsString = counterAsString + counters[level];
        if (level < counters.length - 1) counterAsString = counterAsString + ",";
   }
   System.out.println(counterAsString);
}

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