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

namespace ConsoleApp22
{
    class Program
    {
        static void Main(string[] args)
        {
            var strings = "天时地利人和".ToList();
            Console.WriteLine(string.Join(",",strings.PickRandom(3)));
            Console.Read();
        }
    }



    public static class EnumerableExtension
    {
        public static T PickRandom<T>(this IEnumerable<T> source)
        {
            return source.PickRandom(1).Single();
        }

        public static IEnumerable<T> PickRandom<T>(this IEnumerable<T> source, int count)
        {
            return source.Shuffle().Take(count);
        }

        public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)
        {
            return source.OrderBy(x => Guid.NewGuid());
        }
    }
}