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namespace MPOTD
{
    class Program
    {
        static void Main(string[] args)
        {
            // -1 is locked and 1 is unlocked
            Int16[] doors = new Int16[1000];

            //INIT
            foreach (int door in doors)
            {
                doors[door] = -1;
            }

            for (Int16 unlocker = 1; unlocker <= 1000; unlocker++)
            {
                if (doors[unlocker - 1] % unlocker == 0)
                    doors[unlocker - 1] *= -1;
            }

            Int16 NrUnlocked = 0;
            Int16 NrLocked = 0;

            foreach (int door in doors)
            {
                if (doors[door] == -1)
                    NrLocked++;
                else
                    NrUnlocked++;
            }

            Console.WriteLine(string.Format("Unlocked: {0}. Locked: {1}", NrUnlocked, NrLocked));
            Console.ReadKey();

        }
    }

digimanus wrote:

U31

Quote:

if (doors[unlocker - 1] % unlocker == 0)

for (Int16 unlocker = 1; unlocker <= 1000; unlocker++)
            {
                for (int door = 0; door < 1000; door++)
                {
                    if ((door+1) % unlocker == 0)
                        doors[door] *= -1;
                }
            }