Anagram Algorithm

<?

class backtrack {

  # constructor
  function backtrack($input_array)
  {
    // the array you want to backtrack and get each configuration of
    $this->_array = $input_array;

    // the current configuration of elements
    $this->configuration = array();

    // if $this->taken[$pos] == false, $this->_array[$pos] is yet to be used
    // in the current configuration
    $this->taken = array();

    // set all as NOT taken
    for ($i=0; $i<count($this->_array); $i++) $this->taken[$i] = false;
  }


  # recursive function:
  # fill each position ($pos) in configuration by trying each element from $this->_array
  function do_backtrack($pos)
  {
    // if configuration is complete
    if ($pos == count($this->_array))
    {
      $this->test_configuration();
      return;
    }

    // try fill each position in the configuration with each element in $_array.
    // but we can only use it if it's not in the current configuration (ie its 'taken')
    for ($i=0; $i<count($this->_array); $i++)
    {
      if ($this->taken[$i]) continue;

      $this->configuration[$pos] = $this->_array[$i]; // take it
      $this->taken[$i] = true;      // set it as now taken
      $this->do_backtrack($pos+1);  // continue backtracking to get rest of configuration
      $this->taken[$i] = false;     // set as untaken as we try next configuration
    }
  }


  # we can do something with configuration here since configuration is done
  # but we currently just print it out
  function test_configuration()
  {
    for ($i=0; $i<count($this->_array); $i++) 
        print $this->configuration[$i].' ';
    print '<br>';
  }

}

$btrack = new backtrack(array('1','3','5'));
$btrack->do_backtrack(0);