| map | unordered_map
---------------------------------------------------------
element ordering | strict weak | n/a
| |
common implementation | balanced tree | hash table
| or red-black tree|
| |
search time | log(n) | O(1) if there are no hash collisions
| | Up to O(n) if there are hash collisions
| | O(n) when hash is the same for any key
| |
Insertion time | log(n)+rebalance | Same as search
| |
Deletion time | log(n)+rebalance | Same as search
| |
needs comparators | only operator < | only operator ==
| |
needs hash function | no | yes
| |
common use case | when good hash is| In most other cases.
| not possible or |
| too slow. Or when|
| order is required|