Unordered map vs ordered map

#1

Why do we even use unordered map if ordered map has the same functionality and it is ordered which is even better data accesibility?

#2

mostly because , of search time , in unordered map average search time is o(1) as compared to map which has an average search time of o(logn)

FOR MAP

ordering : - increasing order (by default)
Implementation : Self Balancing BST
search time : logn
insertion time : logn + rebalancing
deletion time : logn + rebalancing

FOR UN-ORDERED MAP

ordering : - no ordering
Implementation : Hash Table
search time : o(1) (Average) || o(n) (worst case)
insertion time : same as search time
deletion time : same as search time

so,
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.

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.

In case of any doubt feel free to ask :slight_smile:
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#3

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