Write a function named rarest that accepts a dictionary from strings to strings as a parameter and returns the value that occurs least frequently in the dictionary.
If there is a tie, return the value that comes earlier in ABC order.
For example, if a variable called names containing the following elements:
{'Alyssa': 'Harding', 'Char': 'Smith', 'Dan': 'Smith', 'Jeff': 'Jones',
'Kasey': 'Jones', 'Kim': 'Smith', 'Morgan': 'Jones', 'Ryan': 'Smith', 'Stef': 'Harding'}
Then a call of rarest(names) would return 'Harding' because that value occurs 2 times, fewer than any other.
Note that we are examining the values in the dictionary, not the keys.
If the dictionary passed is empty, raise a ValueError.
Constraints:
Obey the following restrictions in your solution.
- You may create one additional data structure (list, dictionary, etc.) as auxiliary storage. (You can have as many simple variables as you like.)
- You should not modify the contents of the dictionary passed to your function.
Declare your function in such a way that any caller can be sure that this will not happen.
- Your solution should run in no worse than O(N log N) time, where N is the number of pairs in the dictionary.
