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<?php |
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/** |
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* DataStructures for PHP |
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* |
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* @link https://github.com/SiroDiaz/DataStructures |
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* @copyright Copyright (c) 2017 Siro Díaz Palazón |
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* @license https://github.com/SiroDiaz/DataStructures/blob/master/README.md (MIT License) |
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*/ |
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namespace DataStructures\Trees; |
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use DataStructures\Trees\BinaryTreeAbstract; |
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use DataStructures\Trees\Nodes\AVLNode; |
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/** |
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* AVLTree |
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* |
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* This class is an implementation of a AVL tree. It has as main feature that access, |
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* insertion and deletion is O(log n). This is like a BST but it has a slightly difference |
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* in nodes: contains a height attribute, used to detect when is needed to rebalance the |
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* tree to keep the O(log n). |
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* |
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* @author Siro Diaz Palazon <[email protected]> |
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*/ |
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class AVLTree extends BinaryTreeAbstract { |
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/** |
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* Creates a AVLNode. |
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* |
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* @param int|string $key the key used to store. |
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* @param mixed $data the data. |
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* @param DataStructures\Trees\Nodes\AVLNode|null $parent the parent node. |
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* @param DataStructures\Trees\Nodes\AVLNode|null $left the left child node. |
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* @param DataStructures\Trees\Nodes\AVLNode|null $right the right child node. |
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* |
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* @return DataStructures\Trees\Nodes\AVLNode the new node created. |
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*/ |
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public function createNode($key, $data, $parent = null, $left = null, $right = null) { |
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return new AVLNode($key, $data, $parent, $left, $right); |
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} |
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/** |
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* Does a right rotation. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode $node The node to be |
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* rotated. |
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* @return DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function rightRotation(AVLNode &$node) { |
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$temp = &$node->left; |
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$temp->parent = &$node->parent; |
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$node->left = &$temp->right; |
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if ($node->left !== null) { |
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$node->left->parent = &$node; |
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} |
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$temp->right = &$node; |
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$node->parent = &$temp; |
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// temp took over node's place so now its parent should point to temp |
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if ($temp->parent !== null) { |
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if ($node === $temp->parent->left) { |
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$temp->parent->left = &$temp; |
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} else { |
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$temp->parent->right = &$temp; |
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} |
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} else { |
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$this->root = &$temp; |
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} |
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return $temp; |
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} |
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/** |
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* Does a right rotation. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode $node The node to be |
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* rotated. |
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* @return DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function leftRotation(AVLNode &$node) { |
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$temp = &$node->right; |
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$temp->parent = &$node->parent; |
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$node->right = &$temp->left; |
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if ($node->right !== null) { |
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$node->right->parent = &$node; |
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} |
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$temp->left = &$node; |
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$node->parent = &$temp; |
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// temp took over node's place so now its parent should point to temp |
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if ($temp->parent !== null) { |
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if ($node == $temp->parent->left) { |
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$temp->parent->left = &$temp; |
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} else { |
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$temp->parent->right = &$temp; |
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} |
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} else { |
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$this->root = &$temp; |
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} |
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return $temp; |
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} |
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/** |
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* Double right rotation does first a left rotation of right child node |
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* that detects the imbalance and finally does a right rotation |
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* in the subtree root that detects the imbalance. |
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* Case Right-Left. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode $node The node to be |
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* rotated. |
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* @return DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function doubleRightRotation(AVLNode &$node) { |
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$this->leftRotation($node->left); |
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return $this->rightRotation($node); |
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} |
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/** |
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* Double left rotation does first a right rotation of left child node |
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* that detects the imbalance and finally does a left rotation |
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* in the subtree root that detects the imbalance. |
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* Case Left-Right. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode $node The node to be |
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* rotated. |
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* @return DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function doubleLeftRotation(AVLNode &$node) { |
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$this->rightRotation($node->right); |
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return $this->leftRotation($node); |
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} |
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/** |
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* {@inheritDoc} |
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*/ |
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public function put($key, $data, $update = false) { |
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$nodeInserted = parent::put($key, $data, $update); |
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$this->rebalance($nodeInserted); |
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return $nodeInserted; |
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} |
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/** |
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* {@inheritDoc} |
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*/ |
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public function delete($key) { |
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$nodeDelete = $this->search($key); |
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if($nodeDelete !== null) { |
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$successorNode = parent::delete($key); |
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if($successorNode !== null) { |
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$minimumNode = ($successorNode->right !== null) ? |
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$this->getMinNode($successorNode->right) : $successorNode; |
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$this->recomputeHeight($minimumNode); |
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$this->rebalance($minimumNode); |
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} else { |
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$this->recomputeHeight($nodeDelete->parent); |
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$this->rebalance($nodeDelete->parent); |
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} |
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return $successorNode; |
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} |
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return null; |
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} |
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/** |
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* Rebalance the tree if the difference of height is greater than 1 |
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* between the right and left subtree or reverse. Then it apply a rotation |
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* depending on the type of unbalance. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function rebalance(&$node) { |
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while($node !== null) { |
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$parent = &$node->parent; |
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$leftHeight = ($node->left === null) ? 0 : $node->left->height; |
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$rightHeight = ($node->right === null) ? 0 : $node->right->height; |
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$nodeBalance = $rightHeight - $leftHeight; |
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if($nodeBalance >= 2) { |
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if($node->right->right !== null) { |
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$this->leftRotation($node); |
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return; |
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} else { |
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$this->doubleLeftRotation($node); |
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return; |
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} |
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} else if($nodeBalance <= -2) { |
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if($node->left->left !== null) { |
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$this->rightRotation($node); |
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return; |
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} else { |
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$this->doubleRightRotation($node); |
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return; |
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} |
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} else { |
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$this->adjustHeight($node); |
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} |
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$node = &$parent; |
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} |
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} |
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/** |
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* Recomputes the height of the nodes ascending in the tree. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function recomputeHeight($node) { |
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while($node !== null) { |
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$node->height = $this->maxHeight($node->left, $node->right) + 1; |
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$node = &$node->parent; |
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} |
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} |
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/** |
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* Returns the maximum height between two subtrees. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode|null |
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* @param DataStructures\Trees\Nodes\AVLNode|null |
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* @return int the maximum height |
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*/ |
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private function maxHeight($node1, $node2) { |
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if($node1 !== null && $node2 !== null) { |
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return $node1->height > $node2->height ? $node1->height : $node2->height; |
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} else if($node1 === null) { |
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return $node2 !== null ? $node2->height : 0; |
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} else if($node2 === null) { |
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return $node1 !== null ? $node1->height : 0; |
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} |
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return 0; |
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} |
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/** |
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* Adjust the height of the node. |
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* |
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* @param DataStructures\Trees\Nodes\AVLNode |
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*/ |
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private function adjustHeight(&$node) { |
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$leftHeight = ($node->left === null) ? 0 : $node->left->height; |
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$rightHeight = ($node->right === null) ? 0 : $node->right->height; |
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$node->height = 1 + max($leftHeight, $rightHeight); |
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} |
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} |
If you access a property on an interface, you most likely code against a concrete implementation of the interface.
Available Fixes
Adding an additional type check:
Changing the type hint: