从多个列表生成所有组合 [英] Generate all combinations from multiple lists

问题描述

给定数量未知的列表，每个列表的长度未知，我需要生成一个包含所有可能的唯一组合的单数列表.例如，给定以下列表:

Given an unknown amount of lists, each with an unknown length, I need to generate a singular list with all possible unique combinations. For example, given the following lists:

X: [A, B, C] 
Y: [W, X, Y, Z]

那么我应该可以生成 12 个组合:

Then I should be able to generate 12 combinations:

[AW, AX, AY, AZ, BW, BX, BY, BZ, CW, CX, CY, CZ]

如果添加了包含 3 个元素的第三个列表，我将有 36 种组合，依此类推.

If a third list of 3 elements were added, I'd have 36 combinations, and so forth.

关于如何在 Java 中执行此操作的任何想法?
(伪代码也可以)

Any ideas on how I can do this in Java?
(pseudo code would be fine too)

推荐答案

你需要递归:

假设您的所有列表都在 lists 中，它是一个列表列表.让 result 成为您所需排列的列表.你可以这样实现:

Let's say all your lists are in lists, which is a list of lists. Let result be the list of your required permutations. You could implement it like this:

void generatePermutations(List<List<Character>> lists, List<String> result, int depth, String current) {
    if (depth == lists.size()) {
        result.add(current);
        return;
    }

    for (int i = 0; i < lists.get(depth).size(); i++) {
        generatePermutations(lists, result, depth + 1, current + lists.get(depth).get(i));
    }
}

最终调用将是这样的:

generatePermutations(lists, result, 0, "");

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