Deleting from a HashTable

Question

I'm using tombstone method to delete elements from a hash table.

That is, instead of deallocating the node and reorganizing the hash table I simply put DELETED mark on the deleted index and making it available for further INSERT operations and avoid it from breaking the SEARCH operation.

However, after # of those markers exceed a certain number I actually want to deallocate those nodes and reorganize my table.

I've thought of allocating a new table which has size of: Old Table Size - # of DELETED marks and inserting nodes that are NOT EMPTY and that do not have DELETED mark to this new table using the regular INSERT but this seemed like overkill to me. Is there a better method to do what I want ?

My table uses Open Adressing with hash functions such as Linear Probing, Double Hashing etc.

Answer 1

The algorithm you describe is essentially rehashing, and that's an entirely reasonable approach to the problem. It has the virtue of being exactly the same code as you would use when your hash table occupancy becomes too large.

Estimating an appropriate size for the new table is tricky. It's usually a good idea to not shrink hash tables aggressively after deletions, in case the table is about to start growing again.