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map vs unordered_map in C++

Hungry Hornet answered on June 8, 2020 Popularity 10/10 Helpfulness 10/10

answer map vs unordered_map in C++

map vs unordered_map in C++

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                  | 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.

Popularity 10/10 Helpfulness 10/10 Language cpp

Source: Grepper

Tags: c++ map

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Contributed on Jun 08 2020

Hungry Hornet

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map vs unordered_map in C++

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