如何在Java中的任意数字组上创建笛卡尔积？ [英] How to create cartesian product over arbitrary groups of numbers in Java?

问题描述

假设我有2组数字：

{1, 2, 3},
{4, 5}

我想创建一种算法（使用Java），该算法可输出以下6种组合：

I'd like to create an algorithm (in Java) that outputs the following 6 combinations:

1,4
1,5
2,4
2,5
3,4
3,5

可以有任意数量的组以及每个组中任意数量的成员。因此，在上述示例中，有2个组，第一个组具有3个成员，第二个组具有2个成员。另一个示例如下（3组，第一组3个成员，第二和第三组2个成员）：

There can be an arbitrary number of groups and an arbitrary number of members within each group. So in the above example, there are 2 groups with the first group having 3 members and the second group having 2 members. Another example is the following (3 groups, 3 members in first groups and 2 members in second and third groups):

{1, 2, 3},
{4, 5},
{6, 7}

这将产生以下12个组合：

Which would yield the following 12 combinations:

1,4,6
1,4,7
1,5,6
1,5,7

2,4,6
2,4,7
2,5,6
2,5,7

3,4,6
3,4,7
3,5,6
3,5,7

如何用Java做到这一点？我正在尝试使用递归，并且已经查看了类似的问题，但我仍然即将出现。谢谢您的帮助！ （P.S.这不是用于家庭作业）

How can I do this in Java? I'm trying to use recursion and I've looked at a similar question already but I'm still coming up short. Thanks for the help! (P.S. this is not for a homework assignment)

推荐答案

有点无聊，决定试一试。应该正是您所需要的：

Got a bit bored and decided to give it a shot. Should be exactly what you need:

public static void main(String args[]) {

    ArrayList<int[]> input = new ArrayList<int[]>();
    input.add(new int[] { 1, 2, 3 });
    input.add(new int[] { 4, 5 });
    input.add(new int[] { 6, 7 });

    combine(input, new int[input.size()], 0);
}

private static void combine(ArrayList<int[]> input, int[] current, int k) {

    if(k == input.size()) {
        for(int i = 0; i < k; i++) {
            System.out.print(current[i] + " ");
        }
        System.out.println();
    } else {            
        for(int j = 0; j < input.get(k).length; j++) {
            current[k] = input.get(k)[j];
            combine(input, current, k + 1);
        }       
    }
}

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