The underlying principles of SET and MAP
1. SET
| gather | underlying implementation | Is it in order? | Is it repeatable? | Whether it can be modified | Query efficiency | Addition and deletion efficiency |
|---|---|---|---|---|---|---|
| std::set | red black tree | orderly | no | no | O(logn) | O(logn) |
| std::multiset | red black tree | orderly | Can | no | O(logn) | O(logn) |
| std::unorded_set | Hash table | disorder | no | no | O(1) | O(1) |
2. MAP
| mapping | underlying implementation | Is it in order (key) | Whether to duplicate (key) | Whether to modify (key) | Query efficiency | Addition and deletion efficiency |
|---|---|---|---|---|---|---|
| std::map | red black tree | have | no | no | O(logn) | O(logn) |
| std::multimap | red black tree | have | Can | no | O(logn) | O(logn) |
| std::unordered_map | Hash table | none | no | no | O(1) | O(1) |
3. Summary:
In STL, although the data structures of different underlying implementations are the same, distinguishing different underlying implementations, understanding their similarities and differences, and selecting different underlying implementations according to different application scenarios are of great use in improving program performance and reducing unnecessary calculations. .