C#中字符串集合的排列 [英] Permutations of string collections in C#

问题描述

似乎我又一次被递归算法困住了......

Seems like I'm stuck once again with recursive algorithms...

我的应用程序应该根据用户指定的信息和由如下字符串表示的子文件夹结构将文件排序到不同的文件夹:

My application is supposed to sort files to different folders, according to the information specified by the user and according to a subfolder structure represented by a string like the following:

[ROOT] \ brand \ color \ material \ 

结构字符串中的标签代表集合:

The tags in the structure string represent collections:

假设:

var brand = new List<string> { "Nike", "Adidas", "Reebok" };
var color = new List<string> { "red", "blue", "yellow", "black" };
var material = new List<string> { "leather", "fabric" };

var data = new List<List<string>>() { brand, color, material };

而我想要得到的是:

[ROOT]\Nike\red\leather
[ROOT]\Nike\red\fabric
[ROOT]\Nike\blue\leather
[ROOT]\Nike\blue\fabric
[ROOT]\Nike\yellow\leather
[ROOT]\Nike\yellow\fabric
[ROOT]\Nike\black\leather
[ROOT]\Nike\black\fabric
[ROOT]\Adidas\red\leather
[ROOT]\Adidas\red\fabric
[ROOT]\Adidas\blue\leather
[ROOT]\Adidas\blue\fabric
[ROOT]\Adidas\yellow\leather
[ROOT]\Adidas\yellow\fabric
[ROOT]\Adidas\black\leather
[ROOT]\Adidas\black\fabric
[ROOT]\Reebok\red\leather
[ROOT]\Reebok\red\fabric
[ROOT]\Reebok\blue\leather
[ROOT]\Reebok\blue\fabric
[ROOT]\Reebok\yellow\leather
[ROOT]\Reebok\yellow\fabric
[ROOT]\Reebok\black\leather
[ROOT]\Reebok\black\fabric

问题是数据标签的数量(品牌、颜色、材料)和它们的顺序是事先不知道的，因此需要递归.

The problem is that the amount of data tags (brand, color, material) and their order is not known in advance, hence the need for recursion.

有什么想法吗?

在此先感谢您！

推荐答案

这是 Eric Lippert 的代码.笛卡尔积..

Here is the code By Eric Lippert. Cartesian Product..

http://ericlippert.com/2010/06/28/computing-a-cartesian-product-with-linq/

public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
{
    // base case: 
    IEnumerable<IEnumerable<T>> result = new[] { Enumerable.Empty<T>() };
    foreach (var sequence in sequences)
    {
        var s = sequence; // don't close over the loop variable 
        // recursive case: use SelectMany to build the new product out of the old one 
        result =
            from seq in result
            from item in s
            select seq.Concat(new[] { item });
    }
    return result;
}

<小时>

var result = CartesianProduct(new List<List<string>>() {brand,color,material });

<小时>

用法示例:

---

Usage Example:

var brand = new List<string> { "Nike", "Adidas", "Reebok" };
var color = new List<string> { "red", "blue", "yellow", "black" };
var material = new List<string> { "leather", "fabric" };

foreach (var row in CartesianProduct(new List<List<string>>() { brand, color, material }))
{
    Console.WriteLine(String.Join(",", row));
}

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