从系列中创建独特的双打和三连冠

Question

我有一个Collection(List)项目(String).此集合中的项目数始终介于0到9之间.

我需要从这个集合中创建对和三元组的所有组合.物品在双重或三重中的位置无关紧要.所以{1,2}等于{2,1}.

我怎样才能实现这一目标？也许有一些很好的方法通过LINQ做到这一点？

Answer 1

在下面的代码中,我使用linq生成所有唯一的双精度和三元组.我使用字符串总排序的事实.

这会产生所有双打:

string[] items = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J" };

var combinations = 
    from a in items
    from b in items
    where a.CompareTo(b) < 0
    orderby a, b
    select new { A = a, B = b };

foreach(var pair in combinations)
    Console.WriteLine("({0}, {1})", pair.A, pair.B);

这会生成所有三元组:

string[] items = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J" };

var combinations = 
    from a in items
    from b in items
    from c in items
    where a.CompareTo(b) < 0 && b.CompareTo(c) < 0
    orderby a, b, c
    select new { A = a, B = b, C = c };

foreach(var triplet in combinations)
    Console.WriteLine("({0}, {1}, {2})", triplet.A, triplet.B, triplet.C);

更新: 有一个通用的解决方案来创建特定长度的所有唯一子集,仍然使用linq.但是,您需要一个可以包含子集的返回类型.我创建了一个简单的类LinkedNode,因为对我而言,这与linq结合起来感觉最自然:

void Main()
{
    string[] items = { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J" };

    foreach(var combination in CreateCombinations(items, 5))
        Console.WriteLine("({0})", combination.ToString());
}

private static IEnumerable<LinkedNode> CreateCombinations(string[] items, int length)
{
    if(length == 1)
        return items.Select(item => new LinkedNode { Value = item, Next = null });

    return from a in items 
        from b in CreateCombinations(items, length - 1) 
        where a.CompareTo(b.Value) < 0
        orderby a, b.Value
        select new LinkedNode<T> { Value = a, Next = b };
}

public class LinkedNode
{
    public string Value { get; set; }
    public LinkedNode Next { get; set; }

    public override string ToString()
    {
        return (this.Next == null) ? Value : Value + ", " + Next.ToString();
    }
}

它应该很容易IEnumerable<string>在类上实现LinkedNode,或者将LinkedNodes转换为List<string>或HashSet<string>.请注意,orderby a, b.Value如果订单不重要,您可以删除该行.