When it comes to efficiency, there is a huge difference between maps and unordered maps.
We must know the internal working of both to decide which one is to be used.
| map | unordered_map --------------------------------------------------------- Ordering | increasing order | no ordering | (by default) | Implementation | Self balancing BST | Hash Table | like Red-Black Tree | search time | log(n) | O(1) -> Average | | O(n) -> Worst Case Insertion time | log(n) + Rebalance | Same as search Deletion time | log(n) + Rebalance | Same as search
Use std::map when
- You need ordered data.
- You would have to print/access the data (in sorted order).
- You need predecessor/successor of elements.
- See advantages of BST over Hash Table for more cases.
1 : 1 3 : 5 5 : 10 20 : 100
Use std::unordered_map when
- You need to keep count of some data (Example – strings) and no ordering is required.
- You need single element access i.e. no traversal.
1 : 1 3 : 5 20 : 100 5 : 10
- Different ways to use Const with Reference to a Pointer in C++
- Difference between Informed and Uninformed Search in AI
- Difference between SJF and LJF CPU scheduling algorithms
- Difference between Pilot Testing and Beta Testing
- Difference between SCAN and LOOK Disk scheduling algorithms
- Difference between Seek Time and Transfer Time in Disk Scheduling
- std::to_address in C++ with Examples
- Difference between SIM and RIM instructions in 8085 microprocessor
- Difference between Seek Time and Rotational Latency in Disk Scheduling
- Difference between Preemptive and Non-preemptive CPU scheduling algorithms
- Difference between Seek Time and Disk Access Time in Disk Scheduling
- Difference between Web Designer and Web Developer
- Difference between Static allocation and Stack allocation
- Difference between Information Security and Network Security
- Difference between Static Allocation and Heap Allocation
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to firstname.lastname@example.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.