Separate chaining in hash map

Question

My understanding of separate chaining is that we convert a large number into a small number so that we can use it as an index. But how do we deal with the large index? For example, the current size of my hash_map is 10, a new index calculated by the hash function is 55. So do I need to resize my hash_map every time when the new index is too large?

Thanks!

Answer 1

A common technique is to have a hash function that computes some integer (typically 32-bit or 64-bit) and then to reduce the number to a valid index in the hash table by modding that integer by the table size. For example, if you have a 10-element hash table and your hash code is 55, you'd compute 55 mod 10 = 5 and place the item at index 5.

Depending on your programming language, there may be some edge cases to handle here (say, if the hash code could be negative, you need to ensure that your index is positive), but this general idea works pretty well and is used in many common hash table implementations.