DouKaku?

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        Console.WriteLine(check(new[] { 825, 102, 811, 140, 812, 125, 263 }));
        Console.WriteLine(check(new[] { 824, 102, 811, 140, 810, 155, 263 }));
    }

    static bool check(int[] ls)
    {
        if (ls.Count() <= 1)
        {
            return true;
        }
        else if (ls.First() < ls.Skip(1).First())
        {
            return ls.Skip(1).All(n => ls.First() < n) && check(ls.Skip(1).ToArray());
        }
        else if (ls.First() > ls.Skip(1).First())
        {
            return ls.Skip(1).All(n => ls.First() > n) && check(ls.Skip(1).ToArray());
        }
        else
        {
            return false;
        }
    }
}