PHP SplDoublyLinkedList::shift方法代码示例

 /**
  * Perform a depth-first traversal on the provided graph.
  *
  * @param Digraph $graph
  *   The graph on which to perform the depth-first search.
  * @param DepthFirstVisitorInterface $visitor
  *   The visitor object to use during the traversal.
  * @param object|\SplDoublyLinkedList $start
  *   A vertex, or vertices, to use as start points for the traversal. There
  *   are a few sub-behaviors here:
  *     - If an SplDoublyLinkedList, SplQueue, or SplStack is provided, the
  *       traversal will deque and visit vertices contained therein.
  *     - If a single vertex object is provided, it will be the sole
  *       originating point for the traversal.
  *     - If no value is provided, DepthFirst::find_sources() is called to
  *       search the graph for source vertices. These are place into an
  *       SplQueue in the order in which they are discovered, and traversal
  *       is then run over that queue in the same manner as if calling code
  *       had provided a queue directly. This method *guarantees* that all
  *       vertices in the graph will be visited.
  *
  * @throws RuntimeException
  *   Thrown if an invalid $start parameter is provided.
  */
 public static function traverse(Digraph $graph, DepthFirstVisitorInterface $visitor, $start = NULL)
 {
     if ($start === NULL) {
         $queue = self::find_sources($graph, $visitor);
     } else {
         if ($start instanceof \SplDoublyLinkedList) {
             $queue = $start;
         } else {
             if (is_object($start)) {
                 $queue = new \SplDoublyLinkedList();
                 $queue->push($start);
             }
         }
     }
     if ($queue->isEmpty()) {
         throw new RuntimeException('No start vertex or vertices were provided, and no source vertices could be found in the provided graph.', E_WARNING);
     }
     $visiting = new \SplObjectStorage();
     $visited = new \SplObjectStorage();
     $visitor->beginTraversal();
     $visit = function ($vertex) use($graph, $visitor, &$visit, $visiting, $visited) {
         if ($visiting->contains($vertex)) {
             $visitor->onBackEdge($vertex, $visit);
         } else {
             if (!$visited->contains($vertex)) {
                 $visiting->attach($vertex);
                 $visitor->onStartVertex($vertex, $visit);
                 foreach ($graph->successorsOf($vertex) as $head) {
                     $visitor->onExamineEdge($vertex, $head, $visit);
                     $visit($head);
                 }
                 $visitor->onFinishVertex($vertex, $visit);
                 $visiting->detach($vertex);
                 $visited->attach($vertex);
             }
         }
     };
     // TODO experiment with adding a generator-producing visitor method that yields the queue here
     while (!$queue->isEmpty()) {
         $vertex = $queue->shift();
         $visit($vertex);
     }
     $visitor->endTraversal();
 }

 /**
  * Perform a depth-first traversal on the provided graph.
  *
  * @param DirectedGraph $graph
  *   The graph on which to perform the depth-first search.
  * @param DepthFirstVisitorInterface $visitor
  *   The visitor object to use during the traversal.
  * @param object|\SplDoublyLinkedList $start
  *   A vertex, or vertices, to use as start points for the traversal. There
  *   are a few sub-behaviors here:
  *     - If an SplDoublyLinkedList, SplQueue, or SplStack is provided, the
  *       traversal will deque and visit vertices contained therein.
  *     - If a single vertex object is provided, it will be the sole
  *       originating point for the traversal.
  *     - If no value is provided, DepthFirst::find_sources() is called to
  *       search the graph for source vertices. These are place into an
  *       SplQueue in the order in which they are discovered, and traversal
  *       is then run over that queue in the same manner as if calling code
  *       had provided a queue directly. This method *guarantees* that all
  *       vertices in the graph will be visited.
  *
  * @throws RuntimeException
  *   Thrown if an invalid $start parameter is provided.
  */
 public static function traverse(DirectedGraph $graph, DepthFirstVisitorInterface $visitor, $start = NULL)
 {
     if ($start === NULL) {
         $queue = self::find_sources($graph, $visitor);
     } else {
         if ($start instanceof \SplDoublyLinkedList) {
             $queue = $start;
         } else {
             if (is_object($start)) {
                 $queue = new \SplDoublyLinkedList();
                 $queue->push($start);
             }
         }
     }
     if ($queue->isEmpty()) {
         throw new RuntimeException('No start vertex or vertices were provided, and no source vertices could be found in the provided graph.', E_WARNING);
     }
     $visiting = new \SplObjectStorage();
     $visited = new \SplObjectStorage();
     $visitor->beginTraversal();
     $visit = function ($vertex) use($graph, $visitor, &$visit, $visiting, $visited) {
         if ($visiting->contains($vertex)) {
             $visitor->onBackEdge($vertex, $visit);
         } else {
             if (!$visited->contains($vertex)) {
                 $visiting->attach($vertex);
                 $visitor->onStartVertex($vertex, $visit);
                 $graph->eachAdjacent($vertex, function ($to) use($vertex, &$visit, $visitor) {
                     $visitor->onExamineEdge($vertex, $to, $visit);
                     $visit($to);
                 });
                 $visitor->onFinishVertex($vertex, $visit);
                 $visiting->detach($vertex);
                 $visited->attach($vertex);
             }
         }
     };
     while (!$queue->isEmpty()) {
         $vertex = $queue->shift();
         $visit($vertex);
     }
     $visitor->endTraversal();
 }

// offsetSet($index, $newValue)
// 设置参数索引的节点值, $index必须在链表的键范围中。
// 当一个节点用offsetUnset删掉时时，并不能用offsetSet重新给已删掉的节点设置值，只能对当前可见的节点的值进行修改
$list->offsetSet(3, 'value6');
// offsetUnset($index)
// 删除参数索引的节点
$list->offsetUnset(3);
// add($index, $value);
// 对指定的索引新增一个新值。 当一个节点用offsetUnset时，并没有直接删除，该节点还仍然会保存在内存中。用add可以重新给该节点设置值
$list->add(3, 'first');
// unshift($value)
// 在链表的开始节点插入value作为新的开始节点
$list->unshift('second');
// shift()
// 将链表的第一个移除
$list->shift();
// setIteratorMode(int $mode)
// 设置链表的模式。等价于下面的情况：
// IT_MODE_LIFO: 栈模式，先进后出；IT_MODE_FIFO：队列模式，先进先出
// IT_MODE_DELETE； IT_MODE_KEEP
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO);
// getIteratorMode()
// 获得链表的模式
$list->getIteratorMode();
echo "example: \n";
echo "FIFO (First In First Out): \n";
$list->setIteratorMode(SplDoublyLinkedList::IT_MODE_FIFO);
for ($list->rewind(); $list->valid(); $list->next()) {
    echo $list->current() . "\n";
}
echo "LIFO (First In First Out): \n";

<?php

$dll = new SplDoublyLinkedList();
// errors
try {
    $dll->pop();
} catch (RuntimeException $e) {
    echo "Exception: " . $e->getMessage() . "\n";
}
try {
    $dll->shift();
} catch (RuntimeException $e) {
    echo "Exception: " . $e->getMessage() . "\n";
}
// data consistency
$a = 2;
$dll->push($a);
echo $dll->pop() . "\n";
$a = 2;
$dll->unshift($a);
echo $dll->shift() . "\n";
// peakable
$dll->push(1);
$dll->push(2);
echo $dll->top() . "\n";
echo $dll->bottom() . "\n";
$dll->pop();
$dll->pop();
// countable
$dll->push(NULL);
$dll->push(NULL);

<?php

$ll = new SplDoublyLinkedList();
$ll->push(1);
$ll->push(2);
var_dump($ll->shift(1));

 /** @return the first element of the queue.
  * @note dequeue is an alias of push()
  * @see splDoublyLinkedList::push()
  */
 public function dequeue()
 {
     return parent::shift();
 }

<?php

$dll = new SplDoublyLinkedList();
$dll->unshift('foo');
$dll->unshift('bar');
echo $dll->shift(), PHP_EOL;
$dll->rewind();
echo $dll->current(), PHP_EOL;
$dll->prev();
echo $dll->current(), PHP_EOL;

 /**
  * Shifts a `Token` from the beginning of the list.
  *
  * @return Token The shifted token.
  * @link http://www.php.net/manual/en/spldoublylinkedlist.shift.php
  */
 public function shift()
 {
     return $this->tokens->shift();
 }