Hashing Questions Long
Hash tables with open addressing is a technique used in computer science to implement hash tables, which are data structures that store key-value pairs. In this approach, the hash table is implemented as an array, where each element of the array is called a slot or a bucket. Each slot can either be empty or occupied by a key-value pair.
The concept of open addressing refers to the method used to handle collisions, which occur when two different keys hash to the same slot. Instead of using separate chaining, where each slot contains a linked list of key-value pairs, open addressing aims to resolve collisions by finding an alternative slot within the same array.
To insert a key-value pair into a hash table with open addressing, the hash function is first applied to the key to determine the initial slot. If the slot is empty, the key-value pair is stored in that slot. However, if the slot is occupied, a probing sequence is followed to find the next available slot.
There are different probing techniques used in open addressing, including linear probing, quadratic probing, and double hashing. In linear probing, if the initial slot is occupied, the next slot in the array is checked, and if it is also occupied, the subsequent slots are examined until an empty slot is found. Quadratic probing follows a similar approach but uses a quadratic function to determine the next slot to probe. Double hashing involves using a second hash function to calculate the step size for probing.
When searching for a key in a hash table with open addressing, the hash function is applied to the key to determine the initial slot. If the slot is empty, the key is not present in the hash table. However, if the slot is occupied, the key is compared with the stored key in that slot. If they match, the corresponding value is returned. If not, the probing sequence is followed to search for the key in the subsequent slots until an empty slot is encountered or the key is found.
Deleting a key-value pair from a hash table with open addressing involves marking the slot as deleted instead of actually removing the pair. This is done to maintain the integrity of the probing sequence and ensure that subsequent searches can still find the key.
One advantage of using open addressing in hash tables is that it can achieve better cache performance compared to separate chaining, as all the key-value pairs are stored in a contiguous block of memory. Additionally, open addressing can be more memory-efficient since it does not require additional memory for linked lists.
However, open addressing can suffer from clustering, where consecutive occupied slots form clusters, leading to increased probing and potentially degrading performance. To mitigate this issue, techniques such as rehashing or resizing the hash table can be employed.
In conclusion, hash tables with open addressing provide an efficient way to store and retrieve key-value pairs by resolving collisions through probing sequences. This approach offers advantages in terms of cache performance and memory efficiency, although it may be susceptible to clustering.