Euler P32

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

namespace Euler_P32
{
    class Program
    {
        static void Main(string[] args)
        {
            string inputSet = "123456789";
            RecursiveCombinatorics perms = new RecursiveCombinatorics(inputSet, RecursiveCombinatorics.Mode.Permutation);

            RecursiveCombinatorics combos = new RecursiveCombinatorics(inputSet.Substring(0, inputSet.Length-1), RecursiveCombinatorics.Mode.Combination, 2);
            Console.WriteLine(perms.Count);

            HashSet<int> productList = new HashSet<int>();

            int sum = 0;
            for (int i = 0; i < combos.Count; i++)
            {
                if (combos[i][0] != combos[i][1])
                {
                    for (int j = 0; j < perms.Count; j++)
                    {
                        StringBuilder temp = new StringBuilder(inputSet.Length);
                        for (int k = 0; k < perms[i].Length; k++)
                        {
                            temp.Append(perms[j][k]);
                        }
                        int multiplicand = int.Parse(temp.ToString().Substring(0, (int)combos[i][0][0] - 48));
                        //Console.WriteLine(int.Parse(temp.ToString().Substring(0, (int)varis[i][0][0] - 48)));
                        int multiplier = int.Parse(temp.ToString().Substring((int)combos[i][0][0] - 48, (int)combos[i][1][0] - (int)combos[i][0][0]));
                        //Console.WriteLine(int.Parse(temp.ToString().Substring((int)varis[i][0][0] - 48, (int)varis[i][1][0] - (int)varis[i][0][0])));
                        int product = int.Parse(temp.ToString().Substring((int)combos[i][1][0] - 48));
                        //Console.WriteLine(int.Parse(temp.ToString().Substring((int)varis[i][1][0] - 48)));


                        if (multiplicand * multiplier == product)
                        {
                            if (!productList.Contains(product))
                            {
                                productList.Add(product);
                                sum += product;
                            }
                            Console.WriteLine(temp.ToString());
                            Console.WriteLine(multiplicand + " x " + multiplier + " = " + product);
                        }
                    }
                }
            }
            Console.WriteLine(sum);
        }
    }
}