unordered_map complexity c++ code example
Example 1: map vs unordered_map in C++
| 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
1. You need ordered data.
2. You would have to print/access the data (in sorted order).
3. You need predecessor/successor of elements.
::-> Use std::unordered_map when
1. You need to keep count of some data (Example – strings) and no ordering is required.
2. You need single element access i.e. no traversal.
Example 2: header file for unordered_map in c++
#include<unordered_map>