There are several ways to search a key in std::map or in std::multimap.
To get the iterator of the first occurrence of a key, the find() function can be used. It returns end() if the key does not exist.
std::multimap< int , int > mmp{ {1, 2}, {3, 4}, {6, 5}, {8, 9}, {3, 4}, {6, 7} };
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