size_type count( const Key& key ) const;  (1)  
template< class K > size_type count( const K& x ) const;  (2)  (since C++14) 
Returns the number of elements with key that compares equivalent to the specified argument.
key
. x
. This overload participates in overload resolution only if the qualifiedid Compare::is_transparent
is valid and denotes a type. It allows calling this function without constructing an instance of Key
.key    key value of the elements to count 
x    alternative value to compare to the keys 
Number of elements with key that compares equivalent to key
or x
.
Logarithmic in the size of the container plus linear in the number of elements found.
finds element with specific key (public member function) 

returns range of elements matching a specific key (public member function) 
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