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documentation/cmc/multimap.md

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+# multimap.h
+
+The MultiMap is a Map that allows for multiple keys. This is a data structure that has a very narrow usage. A Map (either TreeMap or HashMap) can also work like a MultiMap if a certain key is mapped to another collection.
+
+`Map<K = int, V = List<int>>` maps an integer to a list of integer.
+
+`MultiMap<K = int, V = int>` maps many integer keys to integer values.
+
+The difference is that in a MultiMap you can store keys that are the same but might be different instances of the same value. This is also relevant if your data type is more complex like a struct where its ID is the same but some other members of this data type are different.
+
+## MultiMap Implementation
+
+The map uses separate chaining and robin hood hashing. Its internal buffer is made of a pair of pointers to entries that represent a linked list. So accessing map->buffer[0] would give the first pair of pointers. Each entry has both a pointer to a previous entry and a next entry. This design choice was made so that every collection in this library has a two-way iterator with a very few exceptions.
+
+Each entry is composed of a Key and a Value. Entries with the same key should always hash to the same linked list. Also, keys that hash to the same bucket will also be in the same linked list.
+
+The order of inserting and removing the same keys will behave like a FIFO. So the first key added will be the first to be removed.