PHP数据的DS扩展

　　PHP7以上才能安装和使用该数据结构扩展，安装比较简单：

1. 运行命令 pecl install ds

2. 在php.ini中添加 extension=ds.so

3. 重启PHP或重载配置

• Collection Interface：包含本库中所有数据结构通用功能的基本interface。 It guarantees that all structures are traversable, countable, and can be converted to json using json_encode().

  Ds\Collection implements Traversable , Countable , JsonSerializable {/* 方法 */abstract public void clear ( void )abstract public Ds\Collection copy ( void )abstract public bool isEmpty ( void )abstract public array toArray ( void )
  }

• Hashable Interface：which allows objects to be used as keys.

  Ds\Hashable {/* 方法 */abstract public bool equals ( object $obj )abstract public mixed hash ( void )
  }

• Sequence Interface：A Sequence 相当于一个一维的数字key数组, with the exception of a few characteristics:

  Use cases:

• Wherever you would use an array as a list (not concerned with keys).

• A more efficient alternative to SplDoublyLinkedList and SplFixedArray.

• Values will always be indexed as [0, 1, 2, …, size - 1].

• Only allowed to access values by index in the range [0, size - 1].

• Vector Class：Vector是自动增长和收缩的连续缓冲区中的一系列值。它是最有效的顺序结构，值的索引直接映射到缓冲区中索引，增长因子不绑定到特定的倍数或指数。其具有以下优缺点：

  Ds\Vector::allocate — Allocates enough memory  a required capacity.::apply — Updates all values by applying a   to  value.::capacity — Returns the  capacity.::clear — Removes all values.::__construct — Creates a  instance.::contains — Determines  the vector contains given values.:: — Returns a shallow  of the vector.:: — Returns the  of values in the collection.::filter — Creates a  vector using a callable to determine which values to .::find — Attempts to find a value'

  　

• 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.

• Capacity does not have to be a power of 2.

• get(), set(), push(), pop() are all O(1).

• 但是 shift(), unshift(), insert() and remove() are all O(n).

• Deque Class：“双端队列”的缩写，也用于Ds\Queue中，拥有head、tail两个指针。The pointers can “wrap around” the end of the buffer, which avoids the need to move other values around to make room. This makes shift and unshift very fast —  something a Ds\Vector can’t compete with. 其具有以下优缺点：

• 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).

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

• Map Class：键值对的连续集合，几乎与数组相同。键可以是任何类型，但必须是唯一的。如果使用相同的键添加到map中，则将替换值。其拥有以下优缺点：

• Keys and values can be any type, including objects.

• Supports array syntax (square brackets).

• Insertion order is preserved.

• Performance and memory efficiency is very similar to an array.

• Automatically frees allocated memory when its size drops low enough.

• Can’t be converted to an array when objects are used as keys.

• Pair Class：A pair is used by Ds\Map to pair keys with values.

  Ds\Pair implements JsonSerializable {/* 方法 */public __construct ([ mixed $key [, mixed $value ]] )
  }

• Set Class：唯一值序列。 This implementation uses the same hash table as Ds\Map, where values are used as keys and the mapped value is ignored.其拥有以下优缺点：

• Values can be any type, including objects.

• Supports array syntax (square brackets).

• Insertion order is preserved.

• Automatically frees allocated memory when its size drops low enough.

• add(), remove() and contains() are all O(1).

• 但Doesn’t support push(), pop(), insert(), shift(), or unshift(). get() is O(n) if there are deleted values in the buffer before the accessed index, O(1) otherwise.

• Stack Class： “last in, first out”集合，只允许在结构顶部进行访问和迭代。

  Ds\Stack implements Ds\Collection {/* 方法 */public void allocate ( int $capacity )public int capacity ( void )public void clear ( void )public Ds\Stack copy ( void )public bool isEmpty ( void )public mixed peek ( void )public mixed pop ( void )public void push ([ mixed $...values ] )public array toArray ( void )
  }

• Queue Class：“first in, first out”集合，只允许在结构前端进行访问和迭代。

  Ds\Queue implements Ds\Collection {/* Constants */const int MIN_CAPACITY = 8 ;/* 方法 */public void allocate ( int $capacity )public int capacity ( void )public void clear ( void )public Ds\Queue copy ( void )public bool isEmpty ( void )public mixed peek ( void )public mixed pop ( void )public void push ([ mixed $...values ] )public array toArray ( void )
  }

• PriorityQueue Class：优先级队列与队列是非常相似的，但值以指定的优先级被推入队列，优先级最高的值总是位于队列的前面，同优先级元素“先入先出”顺序任然保留。在一个PriorityQueue上递代是具有破坏性的，相当于连续弹出操作直到队列为空。Implemented using a max heap.

  Ds\PriorityQueue implements Ds\Collection {/* Constants */const int MIN_CAPACITY = 8 ;/* 方法 */public void allocate ( int $capacity )public int capacity ( void )public void clear ( void )public Ds\PriorityQueue copy ( void )public bool isEmpty ( void )public mixed peek ( void )public mixed pop ( void )public void push ( mixed $value , int $priority )public array toArray ( void )
  }

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