C# 合并只要有交集的所有集合

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

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {

            List<int> list1 = new List<int> { 1, 2, 3 };
            List<int> list2 = new List<int> { 4, 5, 6 };
            List<int> list3 = new List<int> { 1, 4, 7 };


            List<int> list4 = new List<int> { 10, 11, 12 };
            List<int> list5 = new List<int> { 13, 11, 14 };


            List<int> list6 = new List<int> { 16, 17, 18 };
            List<int> list7 = new List<int> { 18, 19, 20 };

            List<List<int>> list = new List<List<int>>();
            list.Add(list1);
            list.Add(list2);
            list.Add(list3);
            list.Add(list4);
            list.Add(list5);
            list.Add(list6);
            list.Add(list7);

            List<int> allint = new List<int>();//所有的集合数据
            HashSet<int> repeated = new HashSet<int>(); //得到没有重复的hashset
            foreach (List<int> item in list)
            {
                foreach (int index in item)
                {
                    if (allint.Contains(index))
                        repeated.Add(index);//得到所有重复的集合的元素
                    allint.Add(index);//得到所有的集合的元素
                }
            }


            foreach (var setkey in repeated)//循环重复的值
            {
                List<int> templist = null;//临时
                List<List<int>> removelist = new List<List<int>>();
                foreach (var item in list)//循环
                {
                    //if (templist == null)
                    //{
                    //    templist = item;
                    //    removelist.Add(item);
                    //}

                    //if (item.Contains(setkey))
                    //{
                    //    removelist.Add(item);
                    //    templist = templist.Union(item).ToList();
                    //}

                    if (item.Contains(setkey))
                    {
                        if (templist == null)
                        {
                            templist = item;
                            removelist.Add(item);
                        }
                        else
                        {
                            removelist.Add(item);
                            templist = templist.Union(item).ToList();
                        }
                    }
                }
                foreach (var item in removelist)
                {
                    list.Remove(item);
                }
                removelist.Clear();
                list.Add(templist);
            }

            foreach (var item in list)
            {
                foreach (var item1 in item)
                {
                    Console.Write(item1 + " , ");
                }
                Console.Write("
");
            }
            Console.ReadKey();
        }


    }
}