如何使用 LINQ 从一组数字中查找 n 项的所有组合?

问题描述

我正在尝试编写一个算法来从一组数字中选择 n 个值的所有组合.

I'm trying to write an algorithm to select all combinations of n values from a set of numbers.

例如，给定集合:1, 2, 3, 7, 8, 9

集合中 2 个值的所有组合是:

All combinations of 2 values from the set is:

(1, 2), (1, 3), (1, 7), (1, 8), (1, 9), (2, 3), (2, 7), (2, 8), (2, 9), (3, 7), (3, 8), (3, 9), (7, 8), (7, 9), (8, 9)

(1, 2), (1, 3), (1, 7), (1, 8), (1, 9), (2, 3), (2, 7), (2, 8), (2, 9), (3, 7), (3, 8), (3, 9), (7, 8), (7, 9), (8, 9)

而 3 是:

(1, 2, 3), (1, 2, 7), (1, 2, 8), (1, 2, 9), (1, 3, 7), (1, 3, 8), (1, 3, 9), (1, 7, 8), (1, 7, 9), (1, 8, 9), (2, 3, 7), (2, 3, 8), (2, 3, 9), (2, 7, 8), (2, 7, 9), (2, 8, 9), (3, 7, 8), (3, 7, 9), (3,8, 9), (7, 8, 9)

(1, 2, 3), (1, 2, 7), (1, 2, 8), (1, 2, 9), (1, 3, 7), (1, 3, 8), (1, 3, 9), (1, 7, 8), (1, 7, 9), (1, 8, 9), (2, 3, 7), (2, 3, 8), (2, 3, 9), (2, 7, 8), (2, 7, 9), (2, 8, 9), (3, 7, 8), (3, 7, 9), (3, 8, 9), (7, 8, 9)

等等！

我目前正在使用方法来产生 2、3 和 4 值组合的返回集，但在我看来，这可以在 LINQ 查询中概括.

I'm currently using methods to to yield return sets of combinations of 2, 3 and 4 values, but it seems to me this could be generalised in a LINQ query.

感谢您的帮助！

推荐答案

用法:

var results = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 }.DifferentCombinations(3);

代码:

public static class Ex
{
    public static IEnumerable<IEnumerable<T>> DifferentCombinations<T>(this IEnumerable<T> elements, int k)
    {
        return k == 0 ? new[] { new T[0] } :
          elements.SelectMany((e, i) =>
            elements.Skip(i + 1).DifferentCombinations(k - 1).Select(c => (new[] {e}).Concat(c)));
    }
}

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