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Showing content from https://cplusplus.com/reference/unordered_map/unordered_multimap/equal_range/ below:

public member function

<unordered_map>

std::unordered_multimap::equal_range 
pair<iterator,iterator>   equal_range ( const key_type& k );pair<const_iterator,const_iterator>   equal_range ( const key_type& k ) const;

Get range of elements with specific key

Returns the bounds of a range that includes all the elements in the container with a key that compares equal to k.

If k does not match any key in the container, an empty range is returned (i.e., a pair where both its members first and second compare equal).



Parameters
k
Key value to be compared.
Member type key_type is the type of the keys for the elements in the container, defined in unordered_multimap as an alias of its first template parameter (Key).

Return value The function returns a pair, where its member pair::first is an iterator to the lower bound of the range, and pair::second is an iterator to its upper bound. The elements in the range are those between these two iterators, including pair::first, but not pair::second.

Member types iterator and const_iterator are forward iterator types.



Example 
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// unordered_multimap::equal_range
#include <iostream>
#include <string>
#include <unordered_map>
#include <algorithm>

typedef std::unordered_multimap<std::string,std::string> stringmap;

int main ()
{
  stringmap myumm = {
     {"orange","FL"},
     {"strawberry","LA"},
     {"strawberry","OK"},
     {"pumpkin","NH"}
  };

  std::cout << "Entries with strawberry:";
  auto range = myumm.equal_range("strawberry");
  for_each (
    range.first,
    range.second,
    [](stringmap::value_type& x){std::cout << " " << x.second;}
  );

  return 0;
}

Output: 
Entries with strawberry: LA OK


Complexity Average case: constant.
Worst case: linear in container size.

Iterator validity No changes.

See also
unordered_multimap::count
Count elements with a specific key (public member function)
unordered_multimap::find
Get iterator to element (public member function)
unordered_multimap::begin
Return iterator to beginning (public member type)

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