HTMLPurifier_Queue

A simple array-backed queue, based off of the classic Okasaki persistent amortized queue. The basic idea is to maintain two stacks: an input stack and an output stack. When the output stack runs out, reverse the input stack and use it as the output stack.

We don't use the SPL implementation because it's only supported on PHP 5.3 and later.

Exercise: Prove that push/pop on this queue take amortized O(1) time.

Exercise: Extend this queue to be a deque, while preserving amortized O(1) time. Some care must be taken on rebalancing to avoid quadratic behaviour caused by repeatedly shuffling data from the input stack to the output stack and back.

• Full name: \HTMLPurifier_Queue

Properties

input

private $input

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output

private $output

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Methods

__construct

public __construct(mixed $input = array()): mixed

Parameters:

Parameter	Type	Description
$input	mixed

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shift

Shifts an element off the front of the queue.

public shift(): mixed

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push

Pushes an element onto the front of the queue.

public push(mixed $x): mixed

Parameters:

Parameter	Type	Description
$x	mixed

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isEmpty

Checks if it's empty.

public isEmpty(): mixed

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Automatically generated on 2025-03-18