Pre-requisite : std::map, std::unordered_map
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 20 : 100 5 : 10 3 : 5
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- Searching in a map using std::map functions in C++
- map::at() and map::swap() in C++ STL
- Code to generate the map of India (with explanation)
- Descending order in Map and Multimap of C++ STL
- Map in C++ Standard Template Library (STL)
- Inserting elements in std::map (insert, emplace and operator )
- Different ways to delete elements in std::map (erase() and clear())
- Hash Table vs STL Map
- Trie memory optimization using hash map
- Map of pairs in STL
- Traversing a map (or unordered_map) in C++ STL
- Operator overloading in C++ to print contents of vector, map, pair, ..
- Map elements of an array to elements of another array
- Check if a key is present in a C++ map or unordered_map
- map::clear() in C++ STL
- map::size() in C++ STL
- map::begin() and end() in C++ STL
- map::empty() in C++ STL
- map::operator in C++ STL
- map::at() in C++ STL
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Improved By : shubhamgupta2956