组合 z

输入a b c d e以及它们对应的数字
比如
a-->1 2 3 
b-->2 3
c-->1
d-->3 4 5
e-->1 3 5
输出a b c d e的可用组合，a b c d e不重复，如
a-->2
b-->3
c-->1
d-->4
e-->5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var dict = new Dictionary<char, List<int>>()
            {
                { ‘a‘, new List<int> { 1, 2, 3 } },
                { ‘b‘, new List<int> { 2, 3 } },
                { ‘c‘, new List<int> { 1 } },
                { ‘d‘, new List<int> { 3, 4, 5 } },
                { ‘e‘, new List<int> { 1, 3, 5 } }
            };
            foo(dict, new Dictionary<char, int>());
        }

        static void foo(Dictionary<char, List<int>> data, Dictionary<char, int> pre)
        {
            if (data.Count == 0)
            {
                Console.WriteLine("found:");
                foreach (var item in pre.OrderBy(x => x.Key))
                    Console.WriteLine("{0} - {1}", item.Key, item.Value);
                return;
            }
            var first = data.OrderBy(x => x.Value.Count()).First();
            foreach (var item in first.Value)
            {
                foo(data.OrderBy(x => x.Value.Count()).Skip(1).ToDictionary(x => x.Key, x => x.Value.Except(new int[] { item }).ToList()), pre.Cast<KeyValuePair<char, int>>().Concat(new KeyValuePair<char, int>[] { new KeyValuePair<char, int>(first.Key, item) }).ToDictionary(x => x.Key, x => x.Value));
            }
        }
    }
}