List<int> list1 = new List<int>() { 1, 2, 5, 12, 10, 4, 5 };

                List<int> list2 = new List<int>() { 0, 1, 4, 2, 7, 8, 9 };

                bool flag1 = CheckList(list1,3);//false
                bool flag2 = CheckList(list2, 3);//true

------解决方案--------------------
C# code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace wanlinq
{
    class Program
    {
        static void Main(string[] args)
        {
            List<int> list1 = new List<int>() { 1, 2, 5, 12, 10, 4, 5 };

            List<int> list2 = new List<int>() { 0, 1, 4, 2, 7, 8, 9 };

            Console.WriteLine(panduan(list1));

            Console.WriteLine(panduan(list2));

            Console.ReadLine();
        }

        static bool panduan(List<int> myinput)
        {
            List<List<int>> re = new List<List<int>>();
            //默认list里面至少有3个元素
            for (int i = 0; i < myinput.Count - 2; i++)
            {
                List<int> re1 = new List<int>();
                re1.Add(myinput[i]);
                re1.Add(myinput[i + 1]);
                re1.Add(myinput[i + 2]);
                re.Add(re1);
            }

            return re.Any(x =>
            {
                if (x[0] + 1 == x[1] && x[0] + 2 == x[2])
                {
                    return true;
                }
                return false;
            }
                );
        }
    }
}

------解决方案--------------------

C# code
 static    bool getRes (IEnumerable<int> list)
          
     {
            
           if (list==null)
            {
                return false;
                
            }

        return   Enumerable.Range(1, list.Count() - 2).Any(index => {
            int first = list.ElementAt(index - 1);
            int mid = list.ElementAt(index);
            int end = list.ElementAt(index + 1);

            return first < mid && mid < end && (mid * 2 == first + end);
            
            });      

     }

------解决方案--------------------

List<int> list1 = new List<int>() { 1, 2, 5, 12, 10, 4, 5 };

           List<int> list2 = new List<int>() { 0, 1, 4, 2, 7, 8, 9 };


           Console.WriteLine(Enumerable.Range(0, list2.Count() - 2).Any(index => list2[index] + list2[index + 2] == 2*list2[index + 1]));
           Console.Read();

------解决方案--------------------

       public static  bool ListCheck(System.Collections.Generic.List<int> list)
       {
           return list.Where((t, index) => index > 0 && index < list.Count() - 1 && t * 2 == list[index - 1] + list[index + 1]).Count() > 0;
       }

------解决方案--------------------
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C# code
 static    bool getRes (IEnumerable<int> list)
          
     {
            
           if (list==null)
            {
                return false;
                
            }

        r……