mirror of
https://github.com/jlengrand/Coding4Interviews.git
synced 2026-03-10 08:11:24 +00:00
109 lines
2.5 KiB
Python
109 lines
2.5 KiB
Python
"""
|
|
HashMap Table Implementation
|
|
|
|
Collisions are not handled in this version.
|
|
|
|
@jlengrand
|
|
2013/11
|
|
"""
|
|
|
|
class HashMap():
|
|
def __init__(self, hash_size=513):
|
|
self._hash_size = hash_size
|
|
self._size = 0
|
|
self.hmap = [None] * self._hash_size
|
|
|
|
def add(self, key, value):
|
|
"""
|
|
Adds the provided value to the hashmap.
|
|
Raises an Exception if a collision is detected
|
|
"""
|
|
my_key = self._hash(key)
|
|
if self.hmap[my_key] == None:
|
|
self.hmap[my_key] = value
|
|
self._size += 1
|
|
else:
|
|
raise Exception("Collision detected at index %d", key)
|
|
|
|
def get(self, key):
|
|
"""
|
|
Finds the element in the hash table that may contain the id for
|
|
the string we are looking for
|
|
"""
|
|
my_key = self._hash(key)
|
|
return self.hmap[my_key]
|
|
|
|
def size(self):
|
|
return self._size
|
|
|
|
def _hash(self, value):
|
|
"""
|
|
Generates a hash for the given value.
|
|
The input is expected to be a String, with only ASCII characters.
|
|
|
|
# hash function taken from HT3.
|
|
# We shift and add : << 4 is a *16
|
|
"""
|
|
if len(value) < 1:
|
|
raise Exception("Size of value must be greater than one")
|
|
|
|
h = 0
|
|
for letter in value:
|
|
h = (h << 4) + ord(letter)
|
|
|
|
return h % self._hash_size
|
|
|
|
class HMTableCollision(HashMap):
|
|
"""
|
|
Extension of the previous HashMap implementation that takes care of
|
|
collisions.
|
|
Instead of having only one slot available per index in the table,
|
|
each index will contain a list. This means several elements can be
|
|
stored with the same index.
|
|
"""
|
|
def __init__(self, hash_size=513):
|
|
self._hash_size = hash_size
|
|
self._size = 0
|
|
self.hmap = [None] * self._hash_size
|
|
|
|
def add(self, key, value):
|
|
"""
|
|
Adds the provided value to the hashmap.
|
|
Raises an Exception if a collision is detected
|
|
"""
|
|
my_key = self._hash(key)
|
|
|
|
if self.hmap[my_key] == None:
|
|
self.hmap[my_key] = [value]
|
|
else:
|
|
self.hmap[my_key].append(value)
|
|
self._size += 1
|
|
|
|
def get(self, key):
|
|
"""
|
|
Finds the element in the hash table that may contain the id for
|
|
the string we are looking for
|
|
"""
|
|
my_key = self._hash(key)
|
|
return self.hmap[my_key]
|
|
|
|
def size(self):
|
|
return self._size
|
|
|
|
def _hash(self, value):
|
|
"""
|
|
Generates a hash for the given value.
|
|
The input is expected to be a String, with only ASCII characters.
|
|
|
|
# hash function taken from HT3.
|
|
# We shift and add : << 4 is a *16
|
|
"""
|
|
if len(value) < 1:
|
|
raise Exception("Size of value must be greater than one")
|
|
|
|
h = 0
|
|
for letter in value:
|
|
h = (h << 4) + ord(letter)
|
|
|
|
return h % self._hash_size
|