Telekom feltöltés

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

namespace ConsoleApplication1
{
  class Program
  {
    static void Main(string[] args)
    {
      /*int[] prices = { 533, 1000, 1060, 1640, 3550, 3559};*/
      int[] prices = { 990, 1000, 1490, 1640, 3550};
      for (int i = 1; i <= prices.Length; i++)
      {
        PrintValidCombinations(prices, i);
      }
      Console.ReadKey();
    }
    private static void PrintValidCombinations(int[] array, int rank)
    {
      PrintValidCombinations(new int[rank + 1], array, 0, rank, 0, array.Length - 1);
    }

    private static void PrintValidCombinations(int[] current, int[] array, int index, int rank, int start, int end)
    {
      if (index == rank)
      {
        int sum = 0;
        int[] prices = new int[current.Length - 1];
        for (int i = 0; i < rank; i++)
        {
          sum += array[current[i]];
          prices[i] = array[current[i]];
        }

        if (IsValid(sum))
        {
          for (int i = 0; i < prices.Length - 1; i++)
          {
            Console.Write("{0} + ", prices[i]);
          }
          Console.WriteLine("{0} = {1}", prices[prices.Length - 1], sum);
        }
      }
      else
      {
        for (int i = start; i <= end; i++)
        {
          current[index] = i;
          PrintValidCombinations(current, array, index + 1, rank, i, end);
        }
      }
    }

    private static bool IsValid(int sum)
    {
      return sum % 100 == 0 && 2500 <= sum && sum < 15000; // az érvényességi idő 2500-tól nő
    }
  }
}