C#LINQ combinatorics:不包含空集的集合的所有组合 [英] C# LINQ combinatorics: All Combinations of a Set without the Empty Set

问题描述

我有一组字符串，我想找到所有可能的字符串组合并将它们添加到列表中.我想最后得到的是每个字符串组合列表的列表，减去空集.

I have a set of strings, and I want to find all possible combinations of the strings and add them to a list. I want to end up with a list of a list of each combination of the strings, minus the empty set.

我创建了一个解决方案，该解决方案使用嵌套的for循环来实现此目的.但是我想更优雅地执行此操作，最好使用LINQ ，而且我不太熟练，因为我还很陌生.

I have created a solution that does this exactly with a nested for loop. However I want to do this more elegantly, preferably with LINQ, and I am not so proficient with it because I'm still pretty new to it.

解决方案应具有2 ^ n-1个组合列表，其中n是原始集合的基数.这是我要寻找的正确示例:

The solution should have 2^n - 1 lists of combinations where n is the cardinality of the original set. Here is a correct example of what I am looking for:

set = {a, b, c}

completedListOfCombinations = 
{
    {a},
    {b},
    {a, b},
    {c},
    {a, c},
    {b, c},
    {a, b, c}
}

这是我在以下帮助下制定的工作，基本但难看的解决方案: https://stackoverflow.com/a/3319652 /3371287

Here is my working, basic but ugly solution that I crafted with help from: https://stackoverflow.com/a/3319652/3371287

List<string> myStrings =  new List<string> { "a", "b", "c" };

var allCombos = new List<List<string>>();

for (int i = 0; i < myStrings.Count; i++)
{
    int subsetCount = allCombos.Count;
    var m = new List<string>();
    m.Add(myStrings[i]);
    allCombos.Add(m);

    for (int j = 0; j < subsetCount; j++)
    {
        string[] subset = new string[allCombos.ElementAt(j).Count + 1];
        allCombos[j].CopyTo(subset, 0);
        subset[subset.Length - 1] = myStrings[i];
        allCombos.Add(subset.ToList());
    }

}

有人可以给我看一个更优雅的解决方案吗?我见过类似的LINQ解决方案，它们创建带有阈值的笛卡尔对和列表，但是我无法根据我的需要对其进行调整.

Can someone show me a more elegant solution for this? I have seen similar LINQ solutions that create Cartesian Pairs and lists with a threshold, but I have not been able to tweak them to what I need.

推荐答案

提供 all 中list中的值是唯一:

  List <String> list = new List<String> { "a", "b", "c" };

  var result = Enumerable
    .Range(1, (1 << list.Count) - 1)
    .Select(index => list.Where((item, idx) => ((1 << idx) & index) != 0).ToList());

要打印:

Console.WriteLine(String
  .Join(Environment.NewLine, result
     .Select(line => String.Join(", ", line))));

结果是

a
b
a, b
c
a, c
b, c
a, b, c

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