Understanding the Complexity of Unordered Maps in C++

Can you explain the time complexity of unordered maps in C++?

Sure! The average time complexity for insertions, deletions, and lookups in an unordered map is O(1). However, in the worst case, it can be O(n) due to hash collisions.

What factors can affect the performance of an unordered map?

Factors include the quality of the hash function, the load factor, and how well the keys are distributed. Poor distribution can lead to more collisions.

How does the load factor influence the unordered map's performance?

The load factor is the ratio of the number of elements to the number of buckets. A higher load factor can lead to more collisions, which degrades performance.

Can you give an example of a good hash function for unordered maps?

A good hash function should distribute keys uniformly across buckets. For example, using std::hash for built-in types is generally effective.

What are some common use cases for unordered maps?

Common use cases include caching, counting occurrences of items, and implementing associative arrays where fast access is needed.