Examples of Definition and Usage of PHP Double Linked List

This paper describes the definition and usage of PHP bidirectional linked list with examples. Share it for your reference, as follows:

Because it is necessary to move a group of data many times, write a bidirectional linked list. But I am really unfamiliar with php. Although there is nothing wrong with testing various methods, I just don't know what the pointers of php language and unset have to pay attention to. Post them for everyone to educate. Efficiency is not tested... ask for understanding ~

<?php
/**
 * ** Double linked list 
 * @author zhiyuan12@
 */
/**
 *  Linked list element node class 
 */
class Node_Element {
  public $pre = NULL; //  Precursor 
  public $next = NULL; //  Succession 
  public $key = NULL; //  Element key value 
  public $data = NULL; //  Node value 
  function __Construct($key, $data) {
    $this->key = $key;
    $this->data = $data;
  }
}
/**
 *  Bidirectional linked list class 
 */
class DoubleLinkedList {
  private $head; //  Head pointer 
  private $tail; //  Tail pointer 
  private $current; //  Current pointer 
  private $len; //  Length of linked list 
  function __Construct() {
    $this->head = self::_getNode ( null, null );
    $this->curelement = $this->head;
    $this->tail = $this->head;
    $len = 0;
  }
  /**
   * @ desc:  Read all nodes of linked list 
   */
  public function readAll() {
    $tmp = $this->head;
    while ( $tmp->next !== null ) {
      $tmp = $tmp->next;
      var_dump ( $tmp->key, $tmp->data );
    }
  }
  public function move($pos1, $pos2) {
    $pos1Node = $this->findPosition ( $pos1 );
    $pos2Node = $this->findPosition ( $pos2 );
    if ($pos1Node !== null && $pos2Node !== null) {
      $tmpKey = $pos1Node->key;
      $tmpData = $pos1Node->data;
      $pos1Node->key = $pos2Node->key;
      $pos1Node->data = $pos2Node->data;
      $pos2Node->key = $tmpKey;
      $pos2Node->data = $tmpData;
      return true;
    }
    return false;
  }
  /**
   * @ desc:  Delete nodes in specified keywords 
   *
   * @param : $key
   *      Linked list elements at specified locations key
   */
  public function delete($key) {
    $pos = $this->find ( $key );
    if ($pos !== null) {
      $tmp = $pos;
      $last = null;
      $first = true;
      while ( $tmp->next !== null && $tmp->next->key === $key ) {
        $tmp = $tmp->next;
        if (! $first) {
          $this->delNode ( $last );
        } else {
          $first = false;
        }
        $last = $tmp;
      }
      if ($tmp->next !== null) {
        $pos->pre->next = $tmp->next;
        $tmp->next->pre = $pos->pre;
      } else {
        $pos->pre->next = null;
      }
      $this->delNode ( $pos );
      $this->delNode ( $tmp );
    }
  }
  /**
   * @ desc:  Delete a node at a specified location 
   *
   * @param : $key
   *      Linked list elements at specified locations key
   */
  public function deletePosition($pos) {
    $tmp = $this->findPosition ( $pos );
    if ($tmp === null) {
      return true;
    }
    if ($tmp === $this->getTail ()) {
      $tmp->pre->next = null;
      $this->delNode ( $tmp );
      return true;
    }
    $tmp->pre->next = $tmp->next;
    $tmp->next->pre = $tmp->pre;
    $this->delNode ( $tmp );
  }
  /**
   * @ desc:  Inserts a node before the specified key value 
   *
   * @param : $key
   *     // Linked list elements at specified locations key
   * @param : $data
   *     // Linked list element data to be inserted 
   * @param : $flag
   *     // Do you want to find locations sequentially for insertion 
   */
  public function insert($key, $data, $flag = true) {
    $newNode = self::_getNode ( $key, $data );
    $tmp = $this->find ( $key, $flag );
    if ($tmp !== null) {
      $newNode->pre = $tmp->pre;
      $newNode->next = $tmp;
      $tmp->pre = $newNode;
      $newNode->pre->next = $newNode;
    } else {
      $newNode->pre = $this->tail;
      $this->tail->next = $newNode;
      $this->tail = $newNode;
    }
    $this->len ++;
  }
  /**
   * @ desc:  Inserts a node before the specified position 
   *
   * @param : $pos
   *      Specify where to insert the linked list 
   * @param : $key
   *      Linked list elements at specified locations key
   * @param : $data
   *      Linked list element data to be inserted 
   */
  public function insertPosition($pos, $key, $data) {
    $newNode = self::_getNode ( $key, $data );
    $tmp = $this->findPosition ( $pos );
    if ($tmp !== null) {
      $newNode->pre = $tmp->pre;
      $newNode->next = $tmp;
      $tmp->pre = $newNode;
      $newNode->pre->next = $newNode;
    } else {
      $newNode->pre = $this->tail;
      $this->tail->next = $newNode;
      $this->tail = $newNode;
    }
    $this->len ++;
    return true;
  }
  /**
   * @ desc:  According to key Value query specifies location data 
   *
   * @param : $key
   *     // Linked list elements at specified locations key
   * @param : $flag
   *     // Whether to find sequentially 
   */
  public function find($key, $flag = true) {
    if ($flag) {
      $tmp = $this->head;
      while ( $tmp->next !== null ) {
        $tmp = $tmp->next;
        if ($tmp->key === $key) {
          return $tmp;
        }
      }
    } else {
      $tmp = $this->getTail ();
      while ( $tmp->pre !== null ) {
        if ($tmp->key === $key) {
          return $tmp;
        }
        $tmp = $tmp->pre;
      }
    }
    return null;
  }
  /**
   * @ desc:  Query the specified location data according to the location 
   *
   * @param : $pos
   *     // Linked list elements at specified locations key
   */
  public function findPosition($pos) {
    if ($pos <= 0 || $pos > $this->len)
      return null;
    if ($pos < ($this->len / 2 + 1)) {
      $tmp = $this->head;
      $count = 0;
      while ( $tmp->next !== null ) {
        $tmp = $tmp->next;
        $count ++;
        if ($count === $pos) {
          return $tmp;
        }
      }
    } else {
      $tmp = $this->tail;
      $pos = $this->len - $pos + 1;
      $count = 1;
      while ( $tmp->pre !== null ) {
        if ($count === $pos) {
          return $tmp;
        }
        $tmp = $tmp->pre;
        $count ++;
      }
    }
    return null;
  }
  /**
   * @ desc:  Returns the linked list header node 
   */
  public function getHead() {
    return $this->head->next;
  }
  /**
   * @ desc:  Returns the tail node of the linked list 
   */
  public function getTail() {
    return $this->tail;
  }
  /**
   * @ desc:  Query the number of linked list nodes 
   */
  public function getLength() {
    return $this->len;
  }
  private static function _getNode($key, $data) {
    $newNode = new Node_Element ( $key, $data );
    if ($newNode === null) {
      echo "new node fail!";
    }
    return $newNode;
  }
  private function delNode($node) {
    unset ( $node );
    $this->len --;
  }
}
$myList = new DoubleLinkedList ();
$myList->insert ( 1, "test1" );
$myList->insert ( 2, "test2" );
$myList->insert ( "2b", "test2-b" );
$myList->insert ( 2, "test2-c" );
$myList->insert ( 3, "test3" );
$myList->insertPosition ( 5, "t", "testt" );
$myList->readAll ();
echo "+++";
$myList->deletePosition(0);
$myList->readAll ();
echo "..." . $myList->getLength ();
var_dump ( $myList->findPosition ( 3 )->data );
?>

Run results:

int(1)
string(5) "test1"
int(2)
string(7) "test2-c"
int(2)
string(5) "test2"
string(2) "2b"
string(7) "test2-b"
string(1) "t"
string(5) "testt"
int(3)
string(5) "test3"
+++int(1)
string(5) "test1"
int(2)
string(7) "test2-c"
int(2)
string(5) "test2"
string(2) "2b"
string(7) "test2-b"
string(1) "t"
string(5) "testt"
int(3)
string(5) "test3"
...6string(5) "test2"

For more readers interested in PHP related contents, please check the topics of this site: "PHP Data Structure and Algorithm Tutorial", "php Programming Algorithm Summary", "php String (string) Usage Summary", "PHP Array (Array) Operation Skills Complete Book", "PHP Common Traversal Algorithms and Skills Summary" and "PHP Mathematical Operation Skills Summary"

I hope this article is helpful to everyone's PHP programming.