Hash Table
- Stores data by mapping inputs to indices using a hash function for fast insertion, retrieval, and deletion.
- Can handle different data types and large amounts of data by mapping into a smaller set of indices.
- Collisions (two inputs mapped to the same index) can occur and are handled with techniques such as chaining or linear probing.
Definition
Section titled “Definition”A hash table is a data structure that allows efficient insertion, retrieval, and deletion of data by using a hash function to map data to a specific index within the table. The hash function takes the data as input and outputs an integer corresponding to an index in the table.
Explanation
Section titled “Explanation”A hash table uses a hash function to convert input data into an integer index where the data is stored. The hash function consistently maps the same input to the same index, enabling quick lookup. Because the function maps inputs to indices, the number of table indices needed can be much smaller than the amount of data stored, which supports efficient storage and access for large datasets. Hash functions can be designed to accept different data types (for example, strings, integers, and floating point numbers), providing flexibility in the kinds of data stored.
The structure has limitations: collisions occur when two pieces of data are mapped to the same index. Collisions can lead to overwriting or loss of data and can decrease efficiency. Common strategies to handle collisions include chaining and linear probing.
Examples
Section titled “Examples”Phone directory example
Section titled “Phone directory example”The data stored are names and corresponding phone numbers. The hash function takes a name as input and outputs an integer representing the index in the table where the name and phone number are stored. For instance, if the name “John Smith” is entered as input, the hash function may output the integer 5. This means the name and phone number for “John Smith” will be stored at index 5 in the table.
Social media database example
Section titled “Social media database example”The data stored are user information such as username, password, and profile information. The hash function takes the username as input and outputs an integer representing the index in the table where the user’s information will be stored. For instance, if the username “jsmith” is entered as input, the hash function may output the integer 20. This means the user’s information for “jsmith” will be stored at index 20 in the table.
Notes or pitfalls
Section titled “Notes or pitfalls”- Collisions: Occur when two pieces of data are mapped to the same index; can result in overwriting or loss of data and reduced efficiency.
- Collision-handling techniques: Chaining and linear probing are used to manage collisions and ensure data is stored properly.
Related terms
Section titled “Related terms”- Hash function
- Collision
- Chaining
- Linear probing