PHP SplHeap key() Function

The SplHeap::key() function is an inbuilt function in PHP which is used to get the current node index.

Generally, the Heap Data Structure are of two types:

• Max-Heap: In a Max-Heap the key present at the root node must be greatest among the keys present at all of its children. The same property must be recursively true for all sub-trees in that Binary Tree.
• Min-Heap: In a Min-Heap the key present at the root node must be minimum among the keys present at all of its children. The same property must be recursively true for all sub-trees in that Binary Tree.

Syntax:

mixed SplHeap::key()

Parameters: This function does not accept any parameter.

Return Value: This function returns the key of current node.

Below programs illustrate the SplHeap::key() function in PHP:

Example 1:

<?php 

// Create a new empty Mix Heap 
$heap = new SplMinHeap(); 

$heap->insert('System'); 
$heap->insert('GFG'); 
$heap->insert('ALGO'); 
$heap->insert('C');
$heap->insert('Geeks'); 
$heap->insert('GeeksforGeeks'); 

// Loop to display the current element of heap
for ($heap->top(); $heap->valid(); $heap->next()) {
    echo "Key => " . $heap->key() 
        . ", Value => " . $heap->current() . "\n";
}

?>

Output:

Key => 5, Value => ALGO
Key => 4, Value => C
Key => 3, Value => GFG
Key => 2, Value => Geeks
Key => 1, Value => GeeksforGeeks
Key => 0, Value => System

Example 2:

<?php 

// Create a new empty Max Heap 
$heap = new SplMaxHeap(); 

$heap->insert('System'); 
$heap->insert('GFG'); 
$heap->insert('ALGO'); 
$heap->insert('C');
$heap->insert('Geeks'); 
$heap->insert('GeeksforGeeks'); 

// Loop to display the current element
// of heap with key
for ($heap->top(); $heap->valid(); $heap->next()) {
    echo "Key => " . $heap->key() 
        . ", Value => " . $heap->current() . "\n";
}

?>

Output:

Key => 5, Value => System
Key => 4, Value => GeeksforGeeks
Key => 3, Value => Geeks
Key => 2, Value => GFG
Key => 1, Value => C
Key => 0, Value => ALGO

Reference: https://www.php.net/manual/en/splheap.key.php