An example code for implementing a doubly linked list in PHP-PHP Tutorial-php.cn

/**
* **Double linked list
* @author zhiyuan12@
* @modified 2012-10-25
* @site: bbs.it-home.org
*/
/**
* Linked list element node class
*/
class Node_Element {
public $pre = NULL; // Precursor
public $next = NULL; // Successor
public $key = NULL; // Element key value
public $data = NULL; // Node value
function __Construct($key, $data) {
$this->key = $key;
$this ->data = $data;
}
}
/**
* Doubly linked list class
*/
class DoubleLinkedList {
private $head; // Head pointer
private $tail; // Tail pointer
private $current; // Current pointer
private $len; // Linked list length
function __Construct() {
$this->head = self::_getNode ( null, null );
$this->curelement = $this->head;
$this->tail = $this->head;
$len = 0;
}
/**
* @ desc: Read all nodes of the 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 the node at the specified keyword
*
* @param: $key
* The linked list element key at the specified position
*/
public function delete($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 the node at the specified position
*
* @param: $key
* The key of the linked list element at the specified position
*/
public function deletePosition($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: Insert the node before the specified key value
*
* @param : $key
* //The linked list element key at the specified position
* @param : $data
* //The linked list element data to be inserted
* @param: $flag
* //Whether to search for positions sequentially for insertion
*/
public function insert($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: Insert the node before the specified position
*
* @param : $pos
* Specify the position to insert into the linked list
* @param : $key
* The key of the linked list element at the specified position
* @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: Query the specified position data based on the key value
*
* @param : $key
* //The linked list element key at the specified position
* @param : $flag
* //Whether to search in order
*/
public function find($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 based on the location
*
* @param: $pos
* //The linked list element key at the specified location
*/
public function findPosition($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: Return the head node of the linked list
*/
public function getHead() {
return $this->head->next;
}
/**
* @desc: Return the tail node of the linked list
*/
public function getTail() {
return $this->tail;
}
/**
* @ desc: Query the number of nodes in the linked list
*/
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 );
?>

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An example code for implementing a doubly linked list in PHP