Hashing Questions Medium
Open addressing and separate chaining are two common methods used to resolve collisions in hashing.
Open addressing, also known as closed hashing, is a collision resolution technique where all the elements are stored directly in the hash table itself. In this method, when a collision occurs, the algorithm searches for the next available empty slot in the hash table and inserts the element there. This is done by using a probing sequence, which determines the order in which the slots are checked. Common probing sequences include linear probing, quadratic probing, and double hashing.
On the other hand, separate chaining is a collision resolution technique where each slot in the hash table contains a linked list of elements. When a collision occurs, the element is inserted at the end of the linked list in the corresponding slot. This allows multiple elements to be stored in the same slot, avoiding the need for searching for an empty slot. To retrieve an element, the hash function is used to determine the slot, and then a search is performed within the linked list to find the desired element.
The main difference between open addressing and separate chaining lies in how collisions are handled. In open addressing, all elements are stored directly in the hash table, which means that the size of the hash table needs to be larger than the number of elements to ensure enough empty slots for collision resolution. In separate chaining, the size of the hash table does not need to be larger than the number of elements, as elements are stored in linked lists within the slots.
Another difference is the impact on performance. Open addressing can lead to more clustering, where consecutive elements are stored in close proximity, which can increase the number of collisions and degrade performance. Separate chaining, on the other hand, does not suffer from clustering as elements are stored in linked lists, but it may have additional memory overhead due to the need for maintaining the linked lists.
In summary, open addressing stores all elements directly in the hash table and uses a probing sequence to resolve collisions, while separate chaining stores elements in linked lists within the hash table slots. The choice between these collision resolution techniques depends on factors such as the expected number of elements, memory constraints, and the desired performance characteristics.