CSE331 Project 5: HashMaps solved


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1 Assignment Overview
For this project you will be implementing a hash map. Maps are associative data structures that pair key
and value items together; by knowing the key it is possible to find the value item associated with the key.
Keys within the map are unique, but values are not; multiple keys can map to the same value. Being a
hash-based map, the expected time for most operations is essentially constant. This class is very similar to
the Python dict class.
Once completed, you will use your hash map to count the number of students who were born in a given
2 Assignment Deliverables
You must turn in completed versions of the following files:
• HashMap.py
Be sure to use the specified file name and to submit your files for grading via Mimir before the project
3 Assignment Specifications
Your task will be to complete the methods listed below:
• len
• load
• buckets
• contains
• getitem
• setitem
• delitem
• clear
• iter
• keys
• year count
Your hash map is an associative data structure with both keys and values. Most of the parameters are
key objects, but setitem takes both a key and a value object. Each of the parameters makes it clear which
parameters are keys and which are values.
setitem adds associations to your map while delitem removes associations. contains determines
whether an association with the given key exists while getitem determines which value item is associated with a given key. len counts the number of associations (that is the number of key-value pairs); do not
count the key and the value separately. buckets counts the number of slots that your map has for storing
items. clear removes all associations from the map. iter enumerates all of the key-value pairs, not just the
keys (this is different from the behavior of Python’s dict class). Instead, the keys function returns a set of
the keys contained in map. The order of the items for both functions is undefined.
Hash tables have a limited number of spaces available to store items. Your load function computes the
load factor: the average number of items per slot. You are required to keep the load factor below 1 at all
times. You may choose to impose a stricter maximum load factor. For your convenience, the constructor
has an optional parameter that sets the maximum load factor. You are allowed to change the default value
of this parameter.
Most of your methods should have an expected amortized constant runtime. The clear, iter, and keys
methods may have a O(n) runtime. You must use O(n) space.
The final method, year count is not a member of your hash map. Instead, this function takes in a hash
map, whose keys are the student names, and values are their birth years, and returns a hash map, where the
key is year and value is the number of students born in that year.
You should include comments where appropriate. In particular, you should describe the method used for
handling hash collisions. You must also add documentation for each of the above methods (as well as for
any helper functions created) in the same style as for the pre-defined methods.
4 Assignment Notes
• Points will be deducted if your solution has warnings of any type.
• You have been supplied with stubs for the required methods. You must complete these methods to
complete the project. You may add more functions than what was provided, but you may not modify
the signatures of the provided methods. You may, however, change the default maximum load
factor provided to your constructor.
• You do have to worry about accessing elements from an empty map.
• You must be able to handle duplicate elements. Duplicate keys are not allowed (but duplicate values
are). Newer associations for a given key replace the older ones.
• Implementations for bool, is empty, and repr have been provided. Note that these rely on the len
and iter functions, so you may want to complete these functions early.
• You have been provided with some unit tests that can be used to assess your solution. There are
additional test cases that will be kept hidden.
• It is your responsibility to check for potential edge cases. The supplied unit tests do not account for
all possible valid inputs
• For the iter method, you may want to use the yield keyword. Remember that the iter function
enumerates key-value pairs, not just the keys. This is different than the behavior of Python dictionaries.
• You may not use the dict class (the built in dictionary type). You are allowed to use the list class
and all of its member functions.
• You may assume that the key objects are hashable. You can use the built-in hash function, which
returns an integer from such an object (note that these integers are completely unrelated to the size
of your map). The value types are not guaranteed to have any kind of special property.