如何生成两个数组的组合? [英] How do I generate combinations of two arrays?

问题描述

给出两个数组，其中一个数组包含变量，而第二个数组包含变量的值，我想获得这两个数组的所有可能组合，例如:

Given two arrays, where array one has variables and array two contains the variable's values, I want to get all possible combinations of those two arrays, for example:

String[] arr = {"E", "A", "C"};
String[] val = {"true", "false"};

数组 arr 可以容纳尽可能多的变量，也可以容纳 val .

Array arr can hold as many variables as possible, and val too.

所需的输出:

E true A true C true
E true A true C false
E true A false C true
E true A false C false

E false A true C true
E false A true C false
E false A false C true
E false A false C false

我尝试了一种递归方法:

I tried a recursion approach:

import java.util.*;

class Main {
    public static void main(String[] args) {
        String[] arr = {"E", "A", "C"};
        String[] val = {"true", "false"};
        printAll(arr, val, 0);
    }

    public static void printAll(String[] x, String[] y, int index) {
        if (x.length == 0) {
            return;
        }
        for (String d : x) {
            for (String val : y) {
                System.out.print(d + " " + val + " ");
                String[] arr2 = Arrays.copyOfRange(x, index + 1, x.length);
                printAll(arr2, y, index);
            }
        }
        System.out.println();
    }
}

但是我得到的输出是:

E true A true C true C false 
A false C true C false 
C true C true C false 
C false C true C false 

E false A true C true C false 
A false C true C false 
C true C true C false 
C false C true C false 

A true A true C true C false 
A false C true C false 
C true C true C false 
C false C true C false 

A false A true C true C false 
A false C true C false 
C true C true C false 
C false C true C false 

C true A true C true C false 
A false C true C false 
C true C true C false 
C false C true C false 

C false A true C true C false 
A false C true C false 
C true C true C false 
C false C true C false 

我希望能够将每行正确的内容保存为 ArrayList 中的元素，但首先我想弄清楚如何正确打印每行.

I want to be able to save each correct line as an element in an ArrayList but first I want to figure out how to print each line correctly.

第二个数组不是常数，每个变量之间是不同的:

The second array is not constant, it differs between each variable:

String[] arr = {"E", "A", "C"};
String[] valE = {"true", "false"};
String[] valA = {"true", "false"};
String[] valB = {"set", "noset", "maybe"};

显然，这无法递归工作，因为我需要沿着变量数组发送每个数组，我通过创建一个包含其特定值的 Variables 对象来实现此目的，因此循环将是:/p>

Obviously this wont work in recursion as I need to send each array along side the variables array, I achieve this by creating a Variables object which contains its specific values, so the loop would be:

for (String d : x) {
    for (String val : d.getValues()) {...}
}

这与主要问题无关，我只是将问题简化为一个简单的情况，其中每个变量都有两个可能的值.

This is not relevant to the main question, I simply reduced the question to a simple case where each variable has two possible values.

推荐答案

您可以使用 streams 迭代地生成两个数组的所有可能组合，如下所示:

You can iteratively generate all possible combinations of two arrays using streams as follows:

String[] arr = {"E", "A", "C"};
String[] val = {"true", "false"};

// an array of possible combinations
String[] comb = Arrays.stream(arr)
        .map(e -> Arrays.stream(val)
                // append each substring
                // with possible combinations
                .map(v -> e + " " + v + " ")
                // return Stream<String[]>
                .toArray(String[]::new))
        // reduce stream of arrays to a single array
        // by sequentially multiplying array pairs
        .reduce((arr1, arr2) -> Arrays.stream(arr1)
                .flatMap(str1 -> Arrays.stream(arr2)
                        .map(str2 -> str1 + str2))
                .toArray(String[]::new))
        .orElse(null);

// output
Arrays.stream(comb).forEach(System.out::println);

E true A true C true 
E true A true C false 
E true A false C true 
E true A false C false 
E false A true C true 
E false A true C false 
E false A false C true 
E false A false C false 

---

^{另请参见:通过替换隐藏的#"数字符号来生成所有可能的字符串组合}

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