Welcome to the Lounge

Prisoners  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20
Survivor   1  1  3  1  3  5  7  1  3  5  7  9 11 13 15  1  3  5  7  9

class Program
{
    static List<int> captures = new List<int>();

    static void Main(string[] args)
    {
        PopulateCaptures();
        int survivor = FindLastOne();

        Console.WriteLine("The last one is: {0}", survivor);

        Console.Write("\n\nHit any key to continue...");
        Console.ReadKey();
    }

    static void PopulateCaptures()
    {
        for (int i = 1; i <= 1000; i++)
            captures.Add(i);
    }

    static int FindLastOne(int startingPosition = 0)
    {
        int retVal = -1;

        List<int> dead = new List<int>();

        if (captures.Count == 1)
        {
            retVal = captures[0];
            return retVal;
        }

        if (startingPosition == 0)
            startingPosition = 2;

        if (startingPosition == 1)
            captures.RemoveAt(0);

        for (int i = 1; i <= captures.Count; i++)
        {
            if (i % 2 == 0)
            {
                dead.Add(captures[i - 1]);
            }
        }

        foreach (int i in dead)
        {
            captures.Remove(i);
        }

        if (captures.Count % 2 != 0)
            startingPosition = 1;

        if (captures.Count == 1)
            retVal = captures[0];
        else
            retVal = FindLastOne(startingPosition);

        return retVal;
    }
}

int index = 1;
var prisoners = Enumerable.Range(1, 1000).ToList();
while (prisoners.Count != 1)
{
    while (index < prisoners.Count)
    {
        prisoners.RemoveAt(index);
        
        // We've killed a prisoner, so the rest of the list has moved up one place.
        // Therefore, we only need to move to the next place to skip the next prisoner.
        index++;
    }
    
    if (index == prisoners.Count + 1)
    {
        // We killed the last one in the list; start the next round with the second in the list:
        index = 1;
    }
    else
    {
        // We killed the second to last; start the next round with the first:
        index = 0;
    }
}

Console.WriteLine(prisoners[0]);

static int FindLastManStanding(int startingPosition = 2)
 {
     int retVal = -1;
     bool lastWasKilled = false;
     List<int> dead = new List<int>();

     if (startingPosition == 1)
         captures.RemoveAt(0);

     int max = captures.Max();

     for (int i = 1; i <= captures.Count; i++)
     {
         if (i % 2 == 0)
         {
             if ( max == captures[i - 1])
                 lastWasKilled = true;

             dead.Add(captures[i - 1]);
         }
     }

     dead.ForEach(x => captures.Remove(x));

     startingPosition = lastWasKilled ? 2 : 1;

     if (captures.Count == 1)
         retVal = captures[0];
     else
         retVal = FindLastManStanding(startingPosition);

     return retVal;
 }

OriginalGriff wrote:

"...to the last I grapple with thee; from hell's heart I stab at thee; for hate's sake I spit my last breath at thee."

var switcher = true;

var range = Enumerable.Range(1,1000).ToList();

while( range.Count > 1)
   range = range.Where(x => (switcher = !switcher) == false).ToList();

range.Dump();  // (LinqPad)