PHP Deque Functions

The Deque is a sequence of values in a contiguous buffer that can grow and shrink automatically. It is a common abbreviation of “double-ended queue” and can be used internally by Ds\Queue.

Two pointers can be used to keep track of a head and tail. The pointers can wrap around the end of a buffer that avoids the need to move other values around to make room. This can make a shift and unshift very fast.

Accessing a value by index can require a translation between an index and its corresponding position in the buffer: ((head + position) % capacity).

Strengths

• Supports array syntax (square brackets).
• Uses less overall memory than an array for the same number of values.
• Automatically frees allocated memory when its size drops low enough.
• get(), set(), push(), pop(), shift(), and unshift() are all O(1).

Weaknesses

• Capacity must be a power of 2.
• insert() and remove() are O(n).

Syntax

Ds\Deque implements Ds\Sequence {
   /* Constants */
   const int MIN_CAPACITY = 8 ;

   /* Methods */
   public void allocate( int $capacity )
   public void apply( callable $callback )
   public int capacity( void )
   public void clear( void )
   public bool contains([ mixed $...values ] )
   public Ds\Deque copy( void )
   public Ds\Deque filter([ callable $callback ] )
   public mixed find( mixed $value )
   public mixed first( void )
   public mixed get( int $index )
   public void insert( int $index [, mixed $...values ] )
   public bool isEmpty( void )
   public string join([ string $glue ] )
   public mixed last( void )
   public Ds\Deque map( callable $callback )
   public Ds\Deque merge( mixed $values )
   public mixed pop( void )
   public void push([ mixed $...values ] )
   public mixed reduce( callable $callback [, mixed $initial ] )
   public mixed remove( int $index )
   public void reverse( void )
   public Ds\Deque reversed( void )
   public void rotate( int $rotations )
   public void set( int $index , mixed $value )
   public mixed shift( void )
   public Ds\Deque slice( int $index [, int $length ] )
   public void sort([ callable $comparator ] )
   public Ds\Deque sorted([ callable $comparator ] )
   public number sum( void )
   public array toArray( void )
   public void unshift([ mixed $values ] )
}

Predefined Constants

Ds\Deque::MIN_CAPACITY