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PHP Tree Support

A class to support bitmask operations.

Install

composer require calabrothers/php-ds-tree

Test

composer install
composer test

Tree Library

Referring to the example tree:

We can introduce the following relevant information to discuss library functionality:

Relationship with other nodes:

For each of this set, an additional set is defined including the argument itself, hence:

Static functions:

As Ds\Deque object, the Tree library provides access to the following operations:

• apply (change the value of the node with a callable)
• filter (select a subset of nodes where the condition is specified with a a callable)
• map (evaluate the nodes value to compute the result given with a callable)

These basic operation are provided as static functions and they operate with a given set of nodes. A magic function provide access to all the previously defined sets.

Example: Let us calculate

    y = 2 x sum( Descendants(A) )

First we need to get a set of nodes given as Descendants(A), then apply a map to double the value. Finally we should sum the elements of the resulting vector.

// Let build some tree...
/*
        A(1)
        /    \    
    B(2)   C(3)
            /   \
            D(4)  E(5)  

*/
$oA = new TreeNode(1);
$oB = new TreeNode(2);
$oC = new TreeNode(3);
$oD = new TreeNode(4);
$oE = new TreeNode(5);

Connect the nodes to form the tree:

// Connects the nodes
$oC->attachChild($oD);
$oC->attachChild($oE);
$oA->attachChild($oB);
$oA->attachChild($oC);

Compute the result:

// Compute 2 x Value, forall the Descendants(A)
$aValue = TreeNode::mapSet(
    $oA->getDescendants(), 
    function ($oValue) {
        return 2 * $oValue;
    }
);
echo $aValue->sum()."\n"; // 28

Referring to the same tree, we can for example get the list of nodes having even value as:

// Get nodes having even value
$aEven = TreeNode::filterSet(
    $oA->getNodes(),
    function ($oValue) {
        return $oValue % 2 == 0;
    }
);

echo "(".$aEven[0]->getValue().",".$aEven[1]->getValue().")"; // (2,4)

Tree Builder

Library provides a convenient class to help construction of trees.

The builder requires a callable, responsible to build new nodes. For example considering a tree of integer values:

$oTreeC = new TreeBuilder(
            function (int $nNumber) : int { 
                return $nNumber; 
            }
        );

With this information, everytime the function begin() is called, a new node is added, forwarding the parameters of the begin() function to the callable function specified in the TreeBuilder constructor.

$oTreeC
    ->begin(1)
        ->begin(2)
        ->end()
        ->begin(3)
            ->begin(4)
            ->end()
            ->begin(5)
            ->end()
        ->end()
    ->end();

It is possible for all the types with a proper __toString() method to see the node values. For instance, in this case:

echo $oTree;
// Result:
┌1
└────2
└────3
    └────4
    └────5

The TreeBuilder is interesting when combined with custom node class, for example, let us consider to build a Tree having as nodes the object of following class:

class TreeNodeExample {
    public $nX;
    public $szY;
    public function __construct(int $nX, string $szY) {
        $this->nX   = $nX;
        $this->szY  = $szY;
    }

    public function myMultiply(int $nZ) {
        $this->nX *= $nZ;
        $this->szY = implode("+", array_fill(0, $nZ,$this->szY));
    }

    public function __toString():string {
        return "($this->nX|$this->szY)";
    }
}

Then we can use a TreeBuilder as:

$oTreeC = new TreeBuilder(
    function (int $nX, string $szY) : TreeNodeExample { 
        return new TreeNodeExample($nX, $szY); 
    }
);

$oTreeC
    ->begin(1, 'one')
        ->begin(2, 'two')
        ->end()
        ->begin(3, 'three')
            ->begin(4, 'four')
                ->myMultiply(2)  // This will call the method of TreeNodeExample! :)
            ->end()
            ->begin(5, 'five')
                ->myMultiply(3)
            ->end()
        ->end()
    ->end();

echo $oTreeC;

┌(1|one)
└────(2|two)
└────(3|three)
    └────(8|four+four)
    └────(15|five+five+five)

Notes

I strongly reccomend to use PHP Ds extension rather than its equivalent Php version. Check https://github.com/php-ds/ext-ds for more information.

Credits

• Vincenzo Calabrò

Support quality code

License

The MIT License (MIT). Please see LICENSE for more information.