What is the time complexity of std::map

Question

What is the time complexity of std::map? And will it degenerate in the worst case? Or it is decide by the implementation, we can\'t know it?

Answer 1

Usually the time complexity is specified for operations. In your case the lookup and insert seems relevant.

See http://www.sgi.com/tech/stl/complexity.html for the guaranteed complexties of the STL containers. And this http://www.sgi.com/tech/stl/AssociativeContainer.html on the Associative Containers.

Another source is found here:

• http://www.cplusplus.com/reference/map/map/find/ --> Logarithmic in size.
• http://www.cplusplus.com/reference/map/map/insert/ --> If a single element is inserted, logarithmic in size in general, but amortized constant if a hint is given and the position given is the optimal.

the lookup of std::map is log(number of elements in the map).