unordered-map

问题 I want to remove elements (histogram bins) from an std::unordered_map (histogram) that fulfills a predictate (histogram bins having zero count) given as a lambda expression as follows std::remove_if(begin(m_map), end(m_map), [](const Bin & bin) { return bin.second == 0; }); but GCC-4.6.1 complains as follows /usr/include/c++/4.6/bits/stl_pair.h:156:2: error: assignment of read-only member ‘std::pair<const unsigned char, unsigned char>::first’ /usr/include/c++/4.6/bits/stl_pair.h: In member

问题 I want to remove elements (histogram bins) from an std::unordered_map (histogram) that fulfills a predictate (histogram bins having zero count) given as a lambda expression as follows std::remove_if(begin(m_map), end(m_map), [](const Bin & bin) { return bin.second == 0; }); but GCC-4.6.1 complains as follows /usr/include/c++/4.6/bits/stl_pair.h:156:2: error: assignment of read-only member ‘std::pair<const unsigned char, unsigned char>::first’ /usr/include/c++/4.6/bits/stl_pair.h: In member

来源： https://stackoverflow.com/questions/25195233/time-complexity-of-iterating-through-a-c-unordered-map

来源： https://stackoverflow.com/questions/25195233/time-complexity-of-iterating-through-a-c-unordered-map

来源： https://stackoverflow.com/questions/25195233/time-complexity-of-iterating-through-a-c-unordered-map

来源： https://stackoverflow.com/questions/25195233/time-complexity-of-iterating-through-a-c-unordered-map

来源： https://stackoverflow.com/questions/25195233/time-complexity-of-iterating-through-a-c-unordered-map

来源： https://stackoverflow.com/questions/34512437/simplest-method-to-check-whether-unordered-map-of-unordered-maps-contains-key

来源： https://stackoverflow.com/questions/60503214/stdunordered-map-bucket-count-after-default-rehash

问题 I need to use a data structure which supports constant time lookups on average. I think that using a std::unordered_map is a good way to do it. My data is a "collection" of numbers. |115|190|380|265| These numbers do not have to be in a particular order. I need to have about O(1) time to determine whether or not a given number exists in this data structure. I have the idea of using a std::unordered_map , which is actually a hash table (am I correct?). So the numbers will be keys, and then I