Rehashing

Rehashing

Rehashing is a process used in hash tables when the load factor (the ratio of the number of elements to the size of the hash table) exceeds a certain threshold. It involves creating a new, larger hash table and rehashing all the elements from the original hash table into the new one. Rehashing helps to maintain a balanced and efficient hash table by reducing the chances of collisions and improving the performance of operations such as insertion, deletion, and searching.

Rehashing Process

Here's how the rehashing process typically works:

Determine the load factor threshold: A load factor threshold is set to determine when rehashing should be triggered. For example, if the load factor exceeds 0.7, indicating that the hash table is 70% full, rehashing may be initiated.

Create a new hash table: When rehashing is triggered, a new, larger hash table is created. The size of the new hash table is usually chosen to be a prime number to reduce the likelihood of clustering and collisions.

Iterate over the original hash table: Each element in the original hash table is iterated over.

Rehash each element: For each element, the hash function is applied to calculate the new index in the new hash table. The element is then inserted into the new hash table at the new index.

Replace the old hash table: Once all elements from the original hash table have been rehashed and inserted into the new hash table, the old hash table is replaced with the new one. The memory occupied by the old hash table is deallocated.


By rehashing, the new hash table can accommodate a larger number of elements, reducing the load factor and improving the efficiency of the hash table operations. Rehashing is typically performed periodically or when the load factor exceeds the predefined threshold to ensure optimal performance of the hash table.