Hash table collisions: why use a linked list if we can use a hash set? One way to deal with the problem of collisions for a hash table is to have a linked list for each bucket. But then the lookup time is no longer constant. Why not use a hash set instead of a linked list? The lookup time would then be constant. For example, in C++ the hash table could be defined as:

unordered_map&lt;int, unordered_set&lt;int&gt;&gt; m;
An hash set is an hash table.  Using an hash set to handle collisions in an hash table is equivalent to using a bigger hash table, with an hashing function which is a combination of the hashing functions of both level.

In other words, you'd probably be better with a bigger initial table (for instance there is no risk of resonance between the two hash functions which could lead to an higher collision rate than expected at the second level).