Example of Joseph's Ring Algorithm Based on Recursive Implementation in PHP

This article describes the Joseph ring algorithm based on recursive implementation of PHP. Share it for your reference, as follows:

Joseph Ring Problem:39 Jews hid in a hole with Josephus and his friends, and 39 Jews decided to die rather than be caught by the enemy. So the method of suicide was decided. 41 people lined up in a circle, and the first person started to report the number. For each time the third person was reported, the person had to commit suicide. Then the next time the count will be re-reported until everyone commits suicide. However, Josephus and his friends did not want to comply. Josephus asked his friends to pretend to comply first. He arranged his friends and himself in the 16th and 31st positions, so he escaped the game of death.

<?php
$num = 41;
$step = 3;
function joseph($arr, $step, $start, $survivors)
{
  foreach($arr as $k => $v)
  {
    if($start % $step === 0)
    {
      unset($arr[$k]);
      $start = 1;
    }
    else
    {
      $start ++;
    }
  }
  if(count($arr) > $survivors)
    return joseph($arr, $step, $start, $survivors);
  else
    return $arr;
}
$i = 0;
$arr = [];
while($i ++ < $num){
  $arr[] = $i;
}
$arr = joseph($arr, 3, 1, 2);
print_r($arr);

Execution results:

Array
(
  [15] => 16
  [30] => 31
)

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