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73 lines
1.5 KiB
Python
73 lines
1.5 KiB
Python
"""
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HashMap Table Implementation
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Collisions are not handled in this version.
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@jlengrand
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2013/11
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"""
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import abc
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class HashMapItem():
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"""
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The type of Object that is ingested by HashMap
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It can be as simple as a String, but must have a get_value() method.
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The get_value method will be used to calculate the hash key
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"""
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__metaclass__ = abc.ABCMeta
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@abc.abstractmethod
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def get_value(self):
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return NotImplementedError("Method has to be implemented by sub classes")
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class HashMap():
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def __init__(self, hash_size=513):
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self._hash_size = hash_size
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self._size = 0
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self.hmap = [None] * self._hash_size
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def add(self, value):
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"""
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Adds the provided value to the hashmap.
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Raises an Exception if a collision is detected
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"""
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key = self._hash(value)
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if self.hmap[key] == None:
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self.hmap[key] = value
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self._size += 1
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else:
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raise Exception("Collision detected at index %d", key)
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# TODO: Keep implementing
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def get(self, value):
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"""
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Finds the element in the hash table that may contain the id for
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the string we are looking for
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"""
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key = self._hash(value)
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return self.hmap[key]
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def size(self):
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return self._size
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def _hash(self, value):
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"""
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Generates a hash for the given value.
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The input is expected to be a String, with only ASCII characters.
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# hash function taken from HT3.
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# We shift and add : << 4 is a *16
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"""
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if len(value) < 1:
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raise Exception("Size of value must be greater than one")
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h = 0
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for letter in value:
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h = (h << 4) + ord(letter)
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return h % self._hash_size
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