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std::unorde...iset::count(3) C++ Standard Libary std::unorde...iset::count(3) NAME std::unordered_multiset::count - std::unordered_multiset::count Synopsis size_type count( const Key& key ) const; (1) (since C++11) template< class K > (2) (since C++20) size_type count( const K& x ) const; 1) Returns the number of elements with key that compares equal to the specified argument key. 2) Returns the number of elements with key that compares equivalent to the specified argument x. This overload participates in overload resolution only if Hash::is_transparent and KeyEqual::is_transparent are valid and each denotes a type. This assumes that such Hash is callable with both K and Key type, and that the KeyEqual is transparent, which, together, allows calling this func- tion without constructing an instance of Key. Parameters key - key value of the elements to count x - a value of any type that can be transparently compared with a key Return value 1) Number of elements with key key. 2) Number of elements with key that compares equivalent to x. Complexity linear in the number of elements with key key on average, worst case linear in the size of the container. Notes Feature-test macro: __cpp_lib_generic_unordered_lookup (for overload (2)) Example // Run this code #include <algorithm> #include <iostream> #include <unordered_set> int main() { std::unordered_multiset set{2, 7, 1, 8, 2, 8, 1, 8, 2, 8}; std::cout << "The set is:\n"; for (int e: set) { std::cout << e << ' '; } const auto [min, max] = std::ranges::minmax(set); std::cout << "\nNumbers [" << min << ".." << max << "] fre- quency:\n"; for (int i{min}; i <= max; ++i) { std::cout << i << ':' << set.count(i) << "; "; } } Possible output: The set is: 8 8 8 8 1 1 7 2 2 2 Numbers [1..8] frequency: 1:2; 2:3; 3:0; 4:0; 5:0; 6:0; 7:1; 8:4; See also find finds element with specific key (C++11) (public member function) contains checks if the container contains element with specific key (C++20) (public member function) equal_range returns range of elements matching a specific key (C++11) (public member function) http://cppreference.com 2022.07.31 std::unorde...iset::count(3)
NAME | Synopsis | Parameters | Return value | Complexity | Notes | Example | Possible output: | See also
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