Hash Table in Data Structure

What is a Hash table in Data Structure?

A hash table is a type of data structure that allows you to easily insert, look up, and delete key-value pairs. In HashTable, a key is a unique integer that is used to index values. In HashTable, the Value is the data linked with the key.

Working of Hash Table

• Initialise Hash Table: Start with an empty array, with each index representing a bucket.
• Insertion: The hash function determines the index for inserting a key-value pair.
• Retrieval: The hash function finds an index for key-value retrieval.
• Collision: Collision occurs when multiple keys map to the same index, which is commonly caused by an inaccurate hash function or a limited array size.

Hash Table Data Structure Algorithm

• Initialize Array: Create a fixed-size array for hash table storage based on the expected key-value pairs.
• Define Hash Function: Creates a unique hash code from the input key.
• Insertion: Use the hash function to calculate the index for key-value pair insertion; handle collisions if the index is already occupied.
• Retrieval: Use the hash function to find the index, then match the stored key to the given key to extract the related value.
• Removal: To remove a key-value pair, use the hash function to obtain the index and then match the stored key with the provided key.

Applications of Hash Table

• Dictionaries
• Caching
• Symbol tables
• Database indexing
• Set membership
• Caching of computed values
• Spell checkers
• Cryptographic data structures

Hash Table Complexity Analysis

Hash tables take O(1) time on average to perform lookup, insertion, and delete operations. However, in the worst-case scenario, these operations may take O(n) time, where n is the number of elements in the table.