Power Crisis

During the power crisis in New Zealand this winter (caused by a shortage of rain and hence low levels in the hydro dams), a contingency scheme was developed to turn off the power to areas of the country in a systematic, totally fair, manner. The country was divided up into N regions (Auckland was region number 1, and Wellington number 13). A number, m, would be picked `at random’, and the power would first be turned off in region 1 (clearly the fairest starting point) and then in every m’th region after that, wrapping around to 1 after N, and ignoring regions already turned off. For example, if N = 17 and m = 5, power would be turned off to the regions in the order:1,6,11,16,5,12,2,9,17,10,4,15,14,3,8,13,7.

The problem is that it is clearly fairest to turn off Wellington last (after all that is where the Electricity headquarters are), so for a given N, the `random’ number m needs to be carefully chosen so that region 13 is the last region selected.

 

Write a program that will read in the number of regions and then determine the smallest number m that will ensure that Wellington (region 13) can function while the rest of the country is blacked out.

 

Input and Output

Input will consist of a series of lines, each line containing the number of regions (N) with . The file will be terminated by a line consisting of a single 0.

Output will consist of a series of lines, one for each line of the input. Each line will consist of the number m according to the above scheme.

 

Sample input

17
0

 

Sample output

7

 

using System;

using System.Collections.Generic;

using System.Text;

using System.IO;

using System.Collections;

 

namespace ConsoleApplication1

{

    class Program

    {

        static void Main(string[] args)

        {

            try

            {

                Console.Write("Enter number of regions: ");

                int numberOfRegions = int.Parse(Console.ReadLine().ToString());

                int[] regionArray = new int[numberOfRegions];

                int randomSeed = 1;

                while(randomSeed != 0)

                {

                    //Initializing the region array

                    for (int i = 0; i < regionArray.Length; i++)

                    {

                        regionArray[i] = 1; //1 is ON, 0 is OFF

                    }

                    int count = 0;

                    for (int i = 0; count != regionArray.Length;)

                    {

                        if (regionArray[i] == 1)

                        {

                            regionArray[i] = 0;

                            count++;

                            if(count == regionArray.Length && (i + 1) == 13)

                            {

                                Console.WriteLine("Random Seed = " + randomSeed);

                                randomSeed = -1;

                                break;

                            }

                        }

                        else

                        {

                            for (int j = 0; j < randomSeed;)

                            {

                                i++;

                                if (i == regionArray.Length)

                                {

                                    i = -1;

                                }

                                else

                                {

                                    if (regionArray[i] == 1)

                                    {

                                        j++;

                                    }

                                }

                            }

                        }

                    }

                    randomSeed++;

                }

            }

            catch (Exception e)

            {

                Console.WriteLine("Error: " + e.Message.ToString());

            }

        }

    }

}

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