Euler problem 41

Last one for today… this isn’t fast code but works…

A bit of a speed up implemented by only checking those which are of length equal to their max character… so there’s not point checking 17 as it’s 2 in length.. so max permitted would be 12… however 132 is fine as it’s 3 in length and has a 3 in it!

_______________________

static void Main(string[] args)
        {
            long max=0;

            for (long i = 1; i < 987654321; i++)
            {
                int len = i.ToString().Length;

               //find max char
                int maxchar = 0;
                foreach (char c in i.ToString())
                {
                    if (c - 48 > maxchar)
                    {
                        maxchar = c - 48;
                    }
                }

               //only check if this could be pandigital - by checking max char and len
                //eg1 17 can't be pandigital as only 2 chars long (eg2 12 =OK, 13=not)

                string s = i.ToString();
                if (maxchar == len && isprime(i))
                {
                 if (s.Split('1').Length==2 && s.Split('2').Length==2 )
                 {
                    if (i.ToString().Length==2 && i > max) {max=i;}
                   
                     if  (s.Split('3').Length==2)
                     {
                         if (i.ToString().Length==3 && i > max) {max=i;}
                         if (s.Split('4').Length==2)
                         {
                             if (i.ToString().Length==4 && i > max) {max=i;}
                              if (s.Split('5').Length==2)
                              {
                                  if (i.ToString().Length==5 && i > max) {max=i;}
                                  if (s.Split('6').Length==2)
                                  {
                                      if (i.ToString().Length==6 && i > max) {max=i;}
                                       if (s.Split('7').Length==2)
                                       {
                                           if (i.ToString().Length==7 && i > max) {max=i;}
                                           if (s.Split('8').Length == 2)
                                           {
                                               if (i.ToString().Length == 8 && i > max) { max = i; }
                                               if (s.Split('9').Length == 2)
                                               {
                                                   if (i.ToString().Length == 9 && i > max) { max = i; }
                                                   break;
                                               }
                                           }
                                       }
                                  }
                              }
                         }
                     }
                 }
                }
            }
            Console.WriteLine(max);
            Console.ReadLine();

        }

 

static bool isprime(long n)
       {
           if (n == 2 || n == 3 || n == 5) { return true; }

          if (n%2==0) {return false;}
          if (n%3 == 0) { return false;}
          if (n%5 == 0) { return false;}

          for (int t = 7; t < Math.Sqrt(n); t++)
          {
              if (n % t== 0)
              {
                  return false;
              }
          }

          return true;

       }