What are the differences between unordered_map and map in C++17?

What are the differences between unordered_map and map in C++17?

In C++17, unordered_map is implemented as a hash table, while map is implemented as a balanced tree. This means that unordered_map offers average constant time complexity for lookups, insertions, and deletions, while map provides logarithmic time complexity.

When should I use unordered_map instead of map?

You should use unordered_map when you need fast access and don't require the elements to be sorted. If you need ordered elements or range queries, then map is the better choice.

Are there any memory usage differences between them?

Yes, unordered_map generally uses more memory due to its underlying hash table structure, which requires additional space for buckets. map, being a tree structure, has a more predictable memory usage pattern.

Can you give an example of when to use each?

Sure! Use unordered_map for scenarios like caching where quick lookups are essential. Use map for applications like maintaining a sorted list of items, such as in a priority queue.