MultiSet that transforms keys.
Input key type.
Indexable key type.
Lookup key type.
Constructor.
Function to transform input key to indexable key.
Number of distinct keys.
Number of values.
Add a key.
Number of occurrences after the operation.
Count occurrences of a key.
Iterate over key and number of occurrences.
Remove a key. No-op if key does not exist.
MultiSet that transforms keys.