Linq 中的组合生成器 [英] Combination Generator in Linq

问题描述

是否可以创建一些 Linq 来生成包含一系列数字的所有可能组合的 List??

Is it possible to create some Linq that generates a List containing all possible combinations of a series of numbers??

如果你输入21"，它会生成一个包含元素的列表:

If you enter "21" it would generate a list with the elements:

list[0] = "21"
list[1] = "22"
list[2] = "11"
list[3] = "12"

(不一定按这个顺序)

我知道您可以使用 range 来执行以下操作:

I understand you can use range to do things like:

List<char> letterRange = Enumerable.Range('a', 'z' - 'a' + 1).Select(i => (Char)i).ToList(); //97 - 122 + 1 = 26 letters/iterations

从 a-z 生成字母表.但我似乎无法将这些知识转移到组合生成器中

Which generates the alphabet from a-z. But I can not seem to transfer this knowledge to make a combination generator

我已经能够用下面的代码弄清楚它，但它看起来太庞大了，我相信它可以用几行来完成.我确实觉得这是一个糟糕的解决方案.

I have been able to figure it out with the following code, but it seems way too bulky and I am sure it can be done with a few lines. It really does feel like a bad solution I have made.

想象一下，如果有帮助，我已经调用了 GetAllCombinations("4321")

Imagine I have called GetAllCombinations("4321") if it helps

public static String[] GetAllCombinations(String s)
{
    var combinations = new string[PossibleCombinations(s.Length)];

    int n = PossibleCombinations(s.Length - 1);

    for (int i = 0; i < s.Length; i++)
    {
        String sub;
        String[] subs;

        if (i == 0)
        {
            sub = s.Substring(1); //Get the first number
        }
        else if (i == s.Length - 1)
        {
            sub = s.Substring(0, s.Length - 1);
        }
        else
        {
            sub = s.Substring(0, i) + s.Substring(i + 1); 
        }

        subs = GetAllCombinations(sub);

        for (int j = 0; j < subs.Length; j++)
        {
            combinations[i * n + j] = s[i] + subs[j];
        }
    }

    return combinations;
}
public static int PossibleCombinations(int n) //Combination possibilities. e.g 1-2-3-4 have 24 different combinations
{
    int result = 1;

    for (int i = 1; i <= n; i++)
        result *= i;

    return result;
}

推荐答案

对于它的价值，尝试这样的事情:

For what it's worth, try something like this:

public static IEnumerable<string> GetPermutations(string s)
{
    if (s.Length > 1)
        return from ch in s
               from permutation in GetPermutations(s.Remove(s.IndexOf(ch), 1))
               select string.Format("{0}{1}", ch, permutation);

    else
        return new string[] { s };
}

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