PHP中的数据结构

　　PHP7以上才能安装和使用数据结构，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:
  • Values will always be indexed as [0, 1, 2, …, size - 1].
  • Only allowed to access values by index in the range [0, size - 1].

  Use cases:

  • Wherever you would use an array as a list (not concerned with keys).
  • A more efficient alternative to SplDoublyLinkedList and SplFixedArray.

• 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：

  • 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).

  Ds\Vector::allocate — Allocates enough memory for a required capacity.
  Ds\Vector::apply — Updates all values by applying a callback function to each value.
  Ds\Vector::capacity — Returns the current capacity.
  Ds\Vector::clear — Removes all values.
  Ds\Vector::__construct — Creates a new instance.
  Ds\Vector::contains — Determines if the vector contains given values.
  Ds\Vector::copy — Returns a shallow copy of the vector.
  Ds\Vector::count — Returns the number of values in the collection.
  Ds\Vector::filter — Creates a new vector using a callable to determine which values to include.
  Ds\Vector::find — Attempts to find a value's index.
  Ds\Vector::first — Returns the first value in the vector.
  Ds\Vector::get — Returns the value at a given index.
  Ds\Vector::insert — Inserts values at a given index.
  Ds\Vector::isEmpty — Returns whether the vector is empty
  Ds\Vector::join — Joins all values together as a string.
  Ds\Vector::jsonSerialize — Returns a representation that can be converted to JSON.
  Ds\Vector::last — Returns the last value.
  Ds\Vector::map — Returns the result of applying a callback to each value.
  Ds\Vector::merge — Returns the result of adding all given values to the vector.
  Ds\Vector::pop — Removes and returns the last value.
  Ds\Vector::push — Adds values to the end of the vector.
  Ds\Vector::reduce — Reduces the vector to a single value using a callback function.
  Ds\Vector::remove — Removes and returns a value by index.
  Ds\Vector::reverse — Reverses the vector in-place.
  Ds\Vector::reversed — Returns a reversed copy.
  Ds\Vector::rotate — Rotates the vector by a given number of rotations.
  Ds\Vector::set — Updates a value at a given index.
  Ds\Vector::shift — Removes and returns the first value.
  Ds\Vector::slice — Returns a sub-vector of a given range.
  Ds\Vector::sort — Sorts the vector in-place.
  Ds\Vector::sorted — Returns a sorted copy.
  Ds\Vector::sum — Returns the sum of all values in the vector.
  Ds\Vector::toArray — Converts the vector to an array.
  Ds\Vector::unshift — Adds values to the front of the vector.
  

  　

• 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 )
  }