Is a PHP array a linked list or an array?

As the most widely used open source programming language in the world, PHP’s data structure is very important. Among them, array is one of the most commonly used data structures in PHP. However, there has always been a question about the nature of PHP arrays: Is it a linked list or an array?

First of all, we need to understand the concepts of linked lists and arrays. A linked list is a collection of nodes, each node contains an address pointing to the next node. This structure can be used to express linear sequences. An array is an ordered collection in which each element can be uniquely identified. Based on these definitions, some people may think that a PHP array is a linked list. but it is not the truth.

In PHP, the essence of an array is a hash table - this is actually a data structure similar to HashMap in Java. A hash table is an array-based data structure in which each element is a key-value pair. In essence, a hash table is a combination of a hash function and a linked list. It is also composed of keys and values, and can quickly find values ​​through keys.

In PHP's memory model, arrays are stored in a structure called "Bucket". Each Bucket structure contains a key and a value, and the Bucket structures corresponding to a pair of key-value pairs can be connected into a linked list. This linked list structure is formed when multiple keys are hashed into the same bucket.

In PHP, we can use arrays to store different types of data, including numbers, strings, objects, etc. This means that in PHP, the elements of the array are not necessarily arranged according to numerical index, but can use any type of key-value correspondence. For example, you can use a string as a key, corresponding to an integer or an object.

The index of PHP array is also more flexible. You can use numbers as keys, strings or objects, etc. Before PHP 5.4, the maximum index value of an array was 2147483647. In PHP 5.4 and later versions, this restriction is removed, that is, the array index can be any integer or string.

Although the essence of PHP arrays is a hash table, since PHP is designed to make it more convenient for developers, array operations in PHP still maintain the syntax of many traditional array operations. This has led some people to think that PHP arrays are linked lists. But from the technical nature, PHP arrays are indeed hash tables.

In PHP, array operations are very common. Since arrays are a very flexible data structure that can store different types of data and support various types of indexes, PHP arrays are very suitable for processing large amounts of data. We can use PHP arrays to implement various common data structures, such as queues, stacks, even graphs, trees, etc.

In general, PHP array is a very powerful data structure. It uses a hash table to store data and solves the problem of hash conflicts through a linked list. Although the operation of PHP arrays is somewhat different from traditional arrays, this does not affect its application as an efficient and flexible data structure. Therefore, we can safely use PHP arrays to store and process our data.

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