.net C# 实现任意List的笛卡尔乘积算法代码

可以扩展到多个集合的情况。类似的例子有，如果a表示某学校学生的集合，b表示该学校所有课程的集合，则a与b的笛卡尔积表示所有可能的选课情况

using system;
using system.collections.generic;
using system.diagnostics;
using system.linq;

namespace 算法
{
    public static class 算法
    {
        /// <summary>
        /// 笛卡尔乘积
        /// </summary>
        public static list<list<t>> cartesianproduct<t>(this list<list<t>> lstsplit)
        {
            int count = 1;
            lstsplit.foreach(item => count *= item.count);
            //count = lstsplit.aggregate(1, (result, next) => result * next.count);

            var lstresult = new list<list<t>>();

            for (int i = 0; i < count; ++i)
            {
                var lsttemp = new list<t>();
                int j = 1;
                lstsplit.foreach(item =>
                {
                    j *= item.count;
                    lsttemp.add(item[(i / (count / j)) % item.count]);
                });
                lstresult.add(lsttemp);
            }
            return lstresult;
        }
    }

    class program
    {
        public static void main()
        {
            stringdemo();
            根据sector生成routing的demo();
            根据sector生成routing的demo2();
        }

        /// <summary>
        /// 简单字符串 笛卡尔乘积
        /// </summary>
        private static void stringdemo()
        {
            var lstsource = new list<list<string>>
            {
                new list<string>() { "a","b","c"},
                new list<string>() { "d","e","f"},
                new list<string>() { "g","h","i"},
            };

            var sw = new stopwatch();
            sw.start();
            var lstresult = lstsource.cartesianproduct();
            console.writeline(sw.elapsed);
        }

        private static void 根据sector生成routing的demo()
        {
            //默认允许输入多个bookingclass,表示使用任意一个都可以。
            var lstsectordef = new list<sector>
            {
                new sector{ seqno=1, bookingclass="a/a1/a2"},
                new sector{ seqno=2, bookingclass="b/b1/b2"},
                new sector{ seqno=3, bookingclass="c/c1/c2"},
                //.....数量不定
            };

            var sw = new stopwatch();
            sw.start();

            var lstsectorgroup = new list<list<sector>>();
            lstsectordef.foreach(item =>
            {
                var lstsector = new list<sector>();
                foreach (var bookingclass in item.bookingclass.split('/'))
                {
                    var sector = item.clone();
                    sector.bookingclass = bookingclass;

                    lstsector.add(sector);
                }
                lstsectorgroup.add(lstsector);
            });

            var lstrouting = lstsectorgroup.cartesianproduct();

            console.writeline(sw.elapsed);
        }

        private static void 根据sector生成routing的demo2()
        {
            //默认允许输入多个bookingclass,表示使用任意一个都可以。
            var lstsectordef = new list<sector>
            {
                new sector{ seqno=1, bookingclass="a1/a2/a3"},
                new sector{ seqno=2, bookingclass="b1/b2/b3"},
                new sector{ seqno=3, bookingclass="c1/c2/c3"},
                //.....数量不定
            };

            var sw = new stopwatch();
            sw.start();

            var lsttemp = new list<list<string>>();
            lstsectordef.foreach(item =>
            {
                lsttemp.add(item.bookingclass.split('/').tolist());
            });

            var lstbookingclassgroup = lsttemp.cartesianproduct();

            var lstrouting = new list<list<sector>>();
            for (int i = 0; i < lstbookingclassgroup.count; i++)
            {
                var lstsector = new list<sector>();
                for (int j = 0; j < lstsectordef.count; j++)
                {
                    var sector = lstsectordef[j].clone();
                    sector.bookingclass = lstbookingclassgroup[i][j];
                    lstsector.add(sector);
                }
                lstrouting.add(lstsector);
            }

            console.writeline(sw.elapsed);
        }

 

    }

    [debuggerdisplay("sector:seqno={seqno},bookingclass={bookingclass}")]
    public class sector
    {
        public int seqno { get; set; }
        public string bookingclass { get; set; }

        public sector clone()
        {
            return this.memberwiseclone() as sector;
        }
    }
}