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hash_map_oa.py
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hash_map_oa.py
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# Name: Will Lambeth
# OSU Email: lambethw@oregonstate.edu
# Course: CS261 - Data Structures
# Assignment: 06 part 2 - Hash map with open addressing
# Due Date: 03 June 2022
# Description: An implementation of a hash map using open addressing to resolve collisions.
from asyncio import proactor_events
from a6_include import (DynamicArray, HashEntry,
hash_function_1, hash_function_2)
class HashMap:
def __init__(self, capacity: int, function) -> None:
"""
Initialize new HashMap that uses
quadratic probing for collision resolution
DO NOT CHANGE THIS METHOD IN ANY WAY
"""
self._buckets = DynamicArray()
for _ in range(capacity):
self._buckets.append(None)
self._capacity = capacity
self._hash_function = function
self._size = 0
def __str__(self) -> str:
"""
Override string method to provide more readable output
DO NOT CHANGE THIS METHOD IN ANY WAY
"""
out = ''
for i in range(self._buckets.length()):
out += str(i) + ': ' + str(self._buckets[i]) + '\n'
return out
def get_size(self) -> int:
"""
Return size of map
DO NOT CHANGE THIS METHOD IN ANY WAY
"""
return self._size
def get_capacity(self) -> int:
"""
Return capacity of map
DO NOT CHANGE THIS METHOD IN ANY WAY
"""
return self._capacity
# ------------------------------------------------------------------ #
def put(self, key: str, value: object) -> None:
"""
Takes a key-value pair and stores it in the hash table.
"""
# Check load factor and resize if needed
load_factor = self.table_load()
if load_factor >= 0.5:
self.resize_table(self._capacity * 2)
# Retrieve index of matching element, or first open index
index = self._get_index(key, False)
element = self._buckets[index]
# If index is open, insert key/value pair there
if element == None or element.is_tombstone:
self._buckets[index] = HashEntry(key, value)
self._size += 1
# Otherwise, update element's value to provided value
else:
element.value = value
def table_load(self) -> float:
"""
Returns the load factor of the current hash table.
"""
empties = self.empty_buckets()
return (self._capacity - empties) / self._capacity
def empty_buckets(self) -> int:
"""
Returns the number of empty buckets in the current hash table.
"""
return (self._capacity - self._size)
def resize_table(self, new_capacity: int) -> None:
"""
Takes an integer and resizes the hash table's capacity to that number.
"""
# Validate new capacity and return if not valid
if new_capacity < 1 or new_capacity < self._size:
return
old_table = self._buckets
# Fill new array with requested number of buckets
self._buckets = DynamicArray()
for _ in range(new_capacity):
self._buckets.append(None)
self._capacity = new_capacity
self._size = 0
# Rehash and populate new array with old values
for i in range(old_table.length()):
entry = old_table[i]
if entry != None and entry.is_tombstone == False:
self.put(entry.key, entry.value)
def get(self, key: str) -> object:
"""
Takes a string and returns the value stored with that string as key,
or None if key does not exist.
"""
index = self._get_index(key)
element = self._buckets[index]
if element != None:
return element.value
else:
return None
def contains_key(self, key: str) -> bool:
"""
Takes a string and returns a boolean denoting whether that string
is a valid key in the current hash table.
"""
index = self._get_index(key)
return self._buckets[index] != None
def remove(self, key: str) -> None:
"""
Takes a key and removes the element with that key from the
hash table. If key is not found, does nothing.
"""
index = self._get_index(key)
element = self._buckets[index]
if element != None:
element.is_tombstone = True
self._size -= 1
def clear(self) -> None:
"""
Removes all stored elements from the hash table, while retaining
its current capacity.
"""
self._size = 0
self._buckets = DynamicArray()
for _ in range(self._capacity):
self._buckets.append(None)
def get_keys(self) -> DynamicArray:
"""
Returns a DynamicArray containing all valid keys for
objects stored in hash table.
"""
keys = DynamicArray()
for i in range(self._capacity):
element = self._buckets[i]
if element != None and element.is_tombstone == False:
keys.append(element.key)
return keys
def _get_index(self, key: str, skip_tombstones: bool=True) -> int:
"""
Helper method that takes a key and an optional parameter to accept/ignore
tombstone values. Returns the index of the given key in the hashmap,
or of the first open index if key is not found.
"""
initial_index = self._hash_function(key) % self._capacity
# Find first hashed index and set up for probing
probe_iterator = 0
index = initial_index
item = self._buckets[index]
# Loop until empty element is found
while item is not None:
# Return if item is found (and isn't a tombstone)
if item.key == key and item.is_tombstone == False:
return index
# Also return on tombstones if operation requires (i.e. put())
elif item.key == key and skip_tombstones == False:
return index
# If not a match or an empty index, increment probe and continue
probe_iterator += 1
index = (initial_index + (probe_iterator ** 2)) % self._capacity
item = self._buckets[index]
# If key not found, return index of first open spot
return index
# ------------------- BASIC TESTING ---------------------------------------- #
if __name__ == "__main__":
print("\nPDF - put example 1")
print("-------------------")
m = HashMap(50, hash_function_1)
for i in range(150):
m.put('str' + str(i), i * 100)
if i % 25 == 24:
print(m.empty_buckets(), m.table_load(), m.get_size(), m.get_capacity())
print("\nPDF - put example 2")
print("-------------------")
m = HashMap(40, hash_function_2)
for i in range(50):
m.put('str' + str(i // 3), i * 100)
if i % 10 == 9:
print(m.empty_buckets(), m.table_load(), m.get_size(), m.get_capacity())
print("\nPDF - table_load example 1")
print("--------------------------")
m = HashMap(100, hash_function_1)
print(m.table_load())
m.put('key1', 10)
print(m.table_load())
m.put('key2', 20)
print(m.table_load())
m.put('key1', 30)
print(m.table_load())
print("\nPDF - table_load example 2")
print("--------------------------")
m = HashMap(50, hash_function_1)
for i in range(50):
m.put('key' + str(i), i * 100)
if i % 10 == 0:
print(m.table_load(), m.get_size(), m.get_capacity())
print("\nPDF - empty_buckets example 1")
print("-----------------------------")
m = HashMap(100, hash_function_1)
print(m.empty_buckets(), m.get_size(), m.get_capacity())
m.put('key1', 10)
print(m.empty_buckets(), m.get_size(), m.get_capacity())
m.put('key2', 20)
print(m.empty_buckets(), m.get_size(), m.get_capacity())
m.put('key1', 30)
print(m.empty_buckets(), m.get_size(), m.get_capacity())
m.put('key4', 40)
print(m.empty_buckets(), m.get_size(), m.get_capacity())
print("\nPDF - empty_buckets example 2")
print("-----------------------------")
m = HashMap(50, hash_function_1)
for i in range(150):
m.put('key' + str(i), i * 100)
if i % 30 == 0:
print(m.empty_buckets(), m.get_size(), m.get_capacity())
print("\nPDF - resize example 1")
print("----------------------")
m = HashMap(20, hash_function_1)
m.put('key1', 10)
print(m.get_size(), m.get_capacity(), m.get('key1'), m.contains_key('key1'))
m.resize_table(30)
print(m.get_size(), m.get_capacity(), m.get('key1'), m.contains_key('key1'))
print("\nPDF - resize example 2")
print("----------------------")
m = HashMap(75, hash_function_2)
keys = [i for i in range(1, 1000, 13)]
for key in keys:
m.put(str(key), key * 42)
print(m.get_size(), m.get_capacity())
for capacity in range(111, 1000, 117):
m.resize_table(capacity)
if m.table_load() >= 0.5:
print("Check that capacity gets updated during resize(); "
"don't wait until the next put()")
m.put('some key', 'some value')
result = m.contains_key('some key')
m.remove('some key')
for key in keys:
# all inserted keys must be present
result &= m.contains_key(str(key))
# NOT inserted keys must be absent
result &= not m.contains_key(str(key + 1))
print(capacity, result, m.get_size(), m.get_capacity(), round(m.table_load(), 2))
print("\nPDF - get example 1")
print("-------------------")
m = HashMap(30, hash_function_1)
print(m.get('key'))
m.put('key1', 10)
print(m.get('key1'))
print("\nPDF - get example 2")
print("-------------------")
m = HashMap(150, hash_function_2)
for i in range(200, 300, 7):
m.put(str(i), i * 10)
print(m.get_size(), m.get_capacity())
for i in range(200, 300, 21):
print(i, m.get(str(i)), m.get(str(i)) == i * 10)
print(i + 1, m.get(str(i + 1)), m.get(str(i + 1)) == (i + 1) * 10)
print("\nPDF - contains_key example 1")
print("----------------------------")
m = HashMap(10, hash_function_1)
print(m.contains_key('key1'))
m.put('key1', 10)
m.put('key2', 20)
m.put('key3', 30)
print(m.contains_key('key1'))
print(m.contains_key('key4'))
print(m.contains_key('key2'))
print(m.contains_key('key3'))
m.remove('key3')
print(m.contains_key('key3'))
print("\nPDF - contains_key example 2")
print("----------------------------")
m = HashMap(75, hash_function_2)
keys = [i for i in range(1, 1000, 20)]
for key in keys:
m.put(str(key), key * 42)
print(m.get_size(), m.get_capacity())
result = True
for key in keys:
# all inserted keys must be present
result &= m.contains_key(str(key))
# NOT inserted keys must be absent
result &= not m.contains_key(str(key + 1))
print(result)
print("\nPDF - remove example 1")
print("----------------------")
m = HashMap(50, hash_function_1)
print(m.get('key1'))
m.put('key1', 10)
print(m.get('key1'))
m.remove('key1')
print(m.get('key1'))
m.remove('key4')
print("\nPDF - clear example 1")
print("---------------------")
m = HashMap(100, hash_function_1)
print(m.get_size(), m.get_capacity())
m.put('key1', 10)
m.put('key2', 20)
m.put('key1', 30)
print(m.get_size(), m.get_capacity())
m.clear()
print(m.get_size(), m.get_capacity())
print("\nPDF - clear example 2")
print("---------------------")
m = HashMap(50, hash_function_1)
print(m.get_size(), m.get_capacity())
m.put('key1', 10)
print(m.get_size(), m.get_capacity())
m.put('key2', 20)
print(m.get_size(), m.get_capacity())
m.resize_table(100)
print(m.get_size(), m.get_capacity())
m.clear()
print(m.get_size(), m.get_capacity())
print("\nPDF - get_keys example 1")
print("------------------------")
m = HashMap(10, hash_function_2)
for i in range(100, 200, 10):
m.put(str(i), str(i * 10))
print(m.get_keys())
m.resize_table(1)
print(m.get_keys())
m.put('200', '2000')
m.remove('100')
m.resize_table(2)
print(m.get_keys())