Arrays Linked Lists Questions Medium
A hash table is a data structure that allows efficient storage and retrieval of key-value pairs. It uses a hash function to map keys to an index in an array, where the corresponding value is stored. The main advantage of a hash table is its constant-time average case complexity for insertion, deletion, and retrieval operations.
Load factor policies in a hash table determine how the table handles the number of elements stored in relation to the size of the underlying array. The load factor is calculated as the ratio of the number of elements to the size of the array.
1. Separate Chaining: In this policy, each index in the array contains a linked list of key-value pairs. When a collision occurs (i.e., two keys map to the same index), the new key-value pair is appended to the linked list at that index. This policy allows multiple elements to be stored at the same index, reducing the chance of collisions. However, it may result in slower performance due to the need to traverse the linked list.
2. Open Addressing: In this policy, when a collision occurs, the hash table searches for the next available index in the array to store the key-value pair. There are different techniques for finding the next available index, such as linear probing (checking the next index sequentially) or quadratic probing (checking indices based on a quadratic function). Open addressing avoids the need for linked lists, resulting in better cache performance. However, it may lead to clustering, where consecutive indices become filled, causing more collisions.
3. Rehashing: Rehashing is a technique used when the load factor exceeds a certain threshold. It involves creating a new, larger array and rehashing all the key-value pairs from the original array into the new one. This helps maintain a low load factor and reduces the chance of collisions. Rehashing can be an expensive operation, but it ensures efficient performance in the long run.
The choice of load factor policy depends on the specific requirements of the application. Separate chaining is often used when the number of elements is expected to be large, while open addressing is suitable for smaller-sized hash tables. Rehashing is employed to dynamically adjust the size of the hash table based on the number of elements, ensuring optimal performance.