N number of people are standing in a circle with person 1 having a gun. He kills the next person and handovers the gun to next alive person. This continues until only one person survives. Find out the survivor.

circle-of-death.php

<?php

class CircleOfDeath
{
	protected $size;

	protected $list;

	protected $current;

	public function __construct($size)
	{
		$this->size = $size;

		$this->list = array_fill(1, $this->size, true);
	}

	public function massKill()
	{
		$this->current = 1;

		while (true)
		{
			$kill = $this->getNext();

			if ($kill)
			{
				$this->list[$kill] = false;

				$next = $this->getNext();

				if ($next)
				{
					$this->current = $next;
				}
				else
				{
					break;
				}
			}
			else
			{
				break;
			}
		}

		return $this->current;
	}

	public function getNext()
	{
		for ($i = $this->current + 1; $i <= $this->size; $i++)
		{
			if ($this->list[$i])
			{
				return $i;
			}
		}

		for ($i = 1; $i < $this->current; $i++)
		{
			if ($this->list[$i])
			{
				return $i;
			}
		}

		return 0;
	}
}


$opts = getopt('s:');

if (isset($opts['s']) || !is_numeric($opts['s']))
{
	$circle = new CircleOfDeath($opts['s']);

	echo 'The survivor is: ' . $circle->massKill();

	echo PHP_EOL;
}
else
{
	echo "\nUSAGE: \n\nphp ./circle-of-death.php -s 100\n\n";
}


/**
 * Command: php ./circle-of-death.php -s 100
 *
 * Output: The survivor is 73.
 */