Question

好像我再次陷入递归算法...

我的应用程序应该根据用户指定的信息并根据由以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：

[ROOT] \ brand \ color \ material \

结构字符串中的标记代表集合：

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 };

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（品牌，颜色，材料）及其订单的数量是事先不知道的，因此需要递归。

有什么想法吗？

提前非常感谢你！

Answer 1

以下是Eric Lippert的代码。笛卡尔积..

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;
}

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

用法示例：

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));
}

Answer 2

这是将当前结果与下一个成员的每个成员交叉连接的简单方法。为此，您还需要创建任何包含[ROOT]的数组。

        var root = new List<string> { "[ROOT]" };
        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>>() { root, brand, color, material };

        IEnumerable<string> lstComb = new List<string> { null };
        foreach (var list in data)
        {
            lstComb = lstComb.SelectMany(o => list.Select(s => $"{o}\\{s}".TrimStart(new char[]{'\\'})));
        }

注意：将项目添加到保存列表的 data 列表时，必须保留顺序。

C＃中字符串集合的排列

2 个答案: