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This article mainly introduces "what does hash mean". In daily operation, I believe many people have doubts about what hash means. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful for you to answer the doubts about "what does hash mean?" Next, please follow the editor to study!

What is a hash table?

A hash table (Hash table, also known as a hash table) is a data structure that is accessed directly based on key code values (Key value). That is, it accesses the record by mapping the key value to a location in the table to speed up the lookup. This mapping function is called a hash function, and the array in which records are stored is called a hash table.

Storage location of the record = f (keyword)

The corresponding relation f here is called hash function, also known as Hash function, which uses hash technology to store records in a continuous storage space, which is called hash table or hash table (Hash table).

The hash table hashtable (key,value) converts Key into an integer number through a fixed algorithm function, namely the so-called hash function, and then takes the remainder of the number as the subscript of the array, and stores the value in the array space with the number as the subscript. (or: any length of input (also known as pre-mapping, pre-image), through the hash algorithm, transformed into a fixed length output, the output is the hash value. This transformation is a compressed mapping, that is, the space of the hash value is usually much smaller than that of the input, and different inputs may be hashed into the same output, and it is not possible to uniquely determine the input value from the hash value. To put it simply, it is a function that compresses a message of any length into a message digest of a fixed length. )

When the hash table is used for query, the hash function is used again to convert key to the corresponding array subscript, and navigate to this space to obtain value, so that the positioning performance of the array can be fully utilized for data positioning.

The array is characterized by easy addressing and difficult insertion and deletion.

The linked list is characterized by difficult addressing and easy insertion and deletion.

So can we combine the characteristics of the two and make a data structure that is easy to address and easy to insert and delete? The answer is yes, this is the hash table we are going to talk about, and there are many different ways to implement the hash table. I will explain the most commonly used method-the zipper method, which we can understand as an array of linked lists, as shown in the figure:

On the left is obviously an array, and each member of the array includes a pointer to the head of a linked list, which may be empty or have many elements. According to some characteristics of the element, we assign the element to different linked lists, and according to these characteristics, we find the correct linked list, and then find the element from the linked list.

Conclusion: computer software science is actually mathematics and an extension of mathematics.

At this point, the study of "what does hash mean" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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