What is a hash table and how do collision resolution strategies work?

• A. Collisions are resolved by chaining or open addressing techniques like linear probing.
• B. Collisions are eliminated by using perfect hashes always.
• C. Collisions are resolved by rehashing with a new hash function when needed.
• D. Collisions cause the table to fail and cannot be resolved.

Answer: (C)

A hash table stores data by mapping keys to positions in an array using a hash function. When two keys map to the same position, a collision occurs. One way to handle this is to rehash the entire table with a different hash function when needed. By selecting a new hash function and rebuilding the table, the keys are redistributed across slots, which can reduce collisions and restore good performance as the table grows or distribution becomes poor. This approach is used in certain hashing schemes, such as universal hashing or strategies that resize and rehash entries. Keep in mind that other common collision-handling methods exist, like chaining items in a bucket or probing to find another slot, but rehashing with a new hash function is a valid way to resolve collisions in some designs.