计算一组n个集合的串联集合

这是我的尝试:

void Main()
{
    IEnumerable<IEnumerable<string>> sets = 
          new[] { 
                  /* a */ new[] { "a", "b", "c" },
                  /* b */ new[] { "1", "2", "3" },
                  /* c */ new[] { "x", "y", "z" }
                };

    var setCombinations = from set in sets
                          select (from itemLength in Enumerable.Range(1, set.Count()).Reverse()
                                  select string.Concat(set.Take(itemLength).ToArray()));

    IEnumerable<string> result = new[] { string.Empty };

    foreach (var list in setCombinations) {
        result = GetCombinations(result, list);
    }
    // do something with the result
}

IEnumerable<string> GetCombinations(IEnumerable<string> root, IEnumerable<string> append) {
    return from baseString in root
           from combination in ((from str in append select baseString + str).Concat(new [] { baseString }))
           select combination;
}

这将产生您想要的:

using System;
using System.Linq;
using System.Collections.Generic;

namespace SO3014119
{
    class Program
    {
        private static IEnumerable<string> GetStringCombinations(
            string prefix, 
            IEnumerable<string>[] collections, int startWithIndex)
        {
            foreach (var element in collections[startWithIndex])
            {
                if (startWithIndex < collections.Length - 1)
                {
                    foreach (var restCombination in
                        GetStringCombinations(prefix + element, collections,
                            startWithIndex + 1))
                    {
                        yield return restCombination;
                    }
                }

                yield return prefix + element;
            }
        }

        public static IEnumerable<string> GetStringCombinations(
            params IEnumerable<string>[] collections)
        {
            while (collections.Length > 0)
            {
                foreach (var comb in GetStringCombinations("", collections, 0))
                    yield return comb;

                // "lop off" head and iterate
                collections = collections.Skip(1).ToArray();
            }
        }

        static void Main(string[] args)
        {
            var a = new string[] { "a1", "a2", "a3" };
            var b = new string[] { "b1", "b2", "b3" };
            var c = new string[] { "c1", "c2", "c3" };

            foreach (string combination in GetStringCombinations(a, b, c))
            {
                Console.Out.WriteLine(combination);
            }
        }
    }
}

这将产生(注意,我更改了输入集合中的条目,以便更容易地看到它们是如何组合的):

a1b1c1
a1b1c2
a1b1c3
a1b1
a1b2c1
a1b2c2
a1b2c3
a1b2
a1b3c1
a1b3c2
a1b3c3
a1b3
a1
a2b1c1
a2b1c2
a2b1c3
a2b1
a2b2c1
a2b2c2
a2b2c3
a2b2
a2b3c1
a2b3c2
a2b3c3
a2b3
a2
a3b1c1
a3b1c2
a3b1c3
a3b1
a3b2c1
a3b2c2
a3b2c3
a3b2
a3b3c1
a3b3c2
a3b3c3
a3b3
a3
b1c1
b1c2
b1c3
b1
b2c1
b2c2
b2c3
b2
b3c1
b3c2
b3c3
b3
c1
c2
c3

解决方案似乎很简单(算法上)

在每个数组a*、b*、c的末尾添加一个extry空字符串*

string[] a* = { "abc","ab","a","" };
string[] b* = { "123","12","1","" };
string[] c* = { "xyz","xy","x","" };

List<string> final = new List<string>();

foreach(string aMember in a*)
foreach(string bMember in b*)
foreach(string cMember in c*)
final.add(aMember+bMember+cMember);

a*、b*和c*末尾的多余空字符串将按所需顺序生成特殊字符串,如a[0](=a[0]+b[3]+c[3])。