Euler Problem 32

Been on hols… so mini break from this.. but had the chance to do one more…

Here we need to find the sum of all products which use numbers 1-9 ONCE in being formed from 2 multipliers and the product itself…

e.g.  4 x 1738 = 6952    => uses 1,2,3,4,5,6,7,8,9

Note we should only include each product (eg 6952) once in the final sum… so I used a list for this.

Other tips – the product and multipliers can be formed into a string.. whose length must be 9.. anything else would mean a double or missing value.

Also we only need test up to 9876 (we could do 9999 but it’d be pointless as there are repeated values there already!)

_________________________

static void Main(string[] args)
       {

           BigInteger sum = 0;
           List<long> found = new List<long>();

           for (long a = 1; a < 9876; a++)
           {
               for (long b = 1; b < 9876; b++)
               {
                   long c = a * b;
                   if (contains1to9once(a, b, c))
                   {
                       if (!found.Contains(c))
                       {
                           sum += c;
                           found.Add(c);
                       }
                   }
               }
           }
           Console.WriteLine(sum);
           Console.ReadLine();

       }

       static bool contains1to9once(long a, long b, long c)
       {
           string s = a.ToString() + b.ToString() + c.ToString();
       
           //has to be 9 chars long only with one of each
           if(s.Length==9 &&
           s.Split('1').Length==2 &&
           s.Split('2').Length==2 &&
           s.Split('3').Length==2 &&
           s.Split('4').Length==2 &&
           s.Split('5').Length==2 &&
           s.Split('6').Length==2 &&
           s.Split('7').Length==2 &&
           s.Split('8').Length==2 &&
           s.Split('9').Length==2)
           {

               return true;
           }
           return false;

       }