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from unittest import TestCase

class HashTable(object):

"""

HashMap Data Type

HashMap() Create a new, empty map. It returns an empty map collection.

put(key, val) Add a new key-value pair to the map. If the key is already in the map then replace

the old value with the new value.

get(key) Given a key, return the value stored in the map or None otherwise.

del_(key) or del map[key] Delete the key-value pair from the map using a statement of the form del map[key].

len() Return the number of key-value pairs stored in the map.

in Return True for a statement of the form key in map, if the given key is in the map, False otherwise.

"""

_empty = object()

_deleted = object()

def __init__(self, size=11):

self.size = size

self._len = 0

self._keys = [self._empty] * size # keys

self._values = [self._empty] * size # values

def put(self, key, value):

initial_hash = hash_ = self.hash(key)

while True:

if self._keys[hash_] is self._empty or self._keys[hash_] is self._deleted:

# can assign to hash_ index

self._keys[hash_] = key

self._values[hash_] = value

self._len += 1

return

elif self._keys[hash_] == key:

# key already exists here, assign over

self._keys[hash_] = key

self._values[hash_] = value

return

hash_ = self._rehash(hash_)

if initial_hash == hash_:

# table is full

raise ValueError("Table is full")

def get(self, key):

initial_hash = hash_ = self.hash(key)

while True:

if self._keys[hash_] is self._empty:

# That key was never assigned

return None

elif self._keys[hash_] == key:

# key found

return self._values[hash_]

hash_ = self._rehash(hash_)

if initial_hash == hash_:

# table is full and wrapped around

return None

def del_(self, key):

initial_hash = hash_ = self.hash(key)

while True:

if self._keys[hash_] is self._empty:

# That key was never assigned

return None

elif self._keys[hash_] == key:

# key found, assign with deleted sentinel

self._keys[hash_] = self._deleted

self._values[hash_] = self._deleted

self._len -= 1

return

hash_ = self._rehash(hash_)

if initial_hash == hash_:

# table is full and wrapped around

return None

def hash(self, key):

return key % self.size

def _rehash(self, old_hash):

"""

linear probing

"""

return (old_hash + 1) % self.size

def __getitem__(self, key):

return self.get(key)

def __delitem__(self, key):

return self.del_(key)

def __setitem__(self, key, value):

self.put(key, value)

def __len__(self):

return self._len

class ResizableHashTable(HashTable):

MIN_SIZE = 8

def __init__(self):

super().__init__(self.MIN_SIZE)

def put(self, key, value):

rv = super().put(key, value)

# increase size of dict * 2 if filled >= 2/3 size (like python dict)

if len(self) >= (self.size * 2) / 3:

self.__resize()

def __resize(self):

keys, values = self._keys, self._values

self.size *= 2 # this will be the new size

self._len = 0

self._keys = [self._empty] * self.size

self._values = [self._empty] * self.size

for key, value in zip(keys, values):

if key is not self._empty and key is not self._deleted:

self.put(key, value)

class TestHashTable(TestCase):

def test_one_entry(self):

m = HashTable(10)

m.put(1, '1')

self.assertEqual('1', m.get(1))

def test_add_entry_bigger_than_table_size(self):

m = HashTable(10)

m.put(11, '1')

self.assertEqual('1', m.get(11))

def test_get_none_if_key_missing_and_hash_collision(self):

m = HashTable(10)

m.put(1, '1')

self.assertEqual(None, m.get(11))

def test_two_entries_with_same_hash(self):

m = HashTable(10)

m.put(1, '1')

m.put(11, '11')

self.assertEqual('1', m.get(1))

self.assertEqual('11', m.get(11))

def test_get_on_full_table_does_halts(self):

# and does not search forever

m = HashTable(10)

for i in range(10, 20):

m.put(i, i)

self.assertEqual(None, m.get(1))

def test_delete_key(self):

m = HashTable(10)

m.put(1, 1)

m.del_(1)

self.assertEqual(None, m.get(1))

def test_delete_key_and_reassign(self):

m = HashTable(10)

m.put(1, 1)

del m[1]

m.put(1, 2)

self.assertEqual(2, m.get(1))

def test_assigning_to_full_table_throws_error(self):

m = HashTable(3)

m.put(1, 1)

m.put(2, 2)

m.put(3, 3)

with self.assertRaises(ValueError):

m.put(4, 4)

def test_len_trivial(self):

m = HashTable(10)

self.assertEqual(0, len(m))

for i in range(10):

m.put(i, i)

self.assertEqual(i + 1, len(m))

def test_len_after_deletions(self):

m = HashTable(10)

m.put(1, 1)

self.assertEqual(1, len(m))

m.del_(1)

self.assertEqual(0, len(m))

m.put(11, 42)

self.assertEqual(1, len(m))

def test_resizable_hash_table(self):

m = ResizableHashTable()

self.assertEqual(ResizableHashTable.MIN_SIZE, m.size)

for i in range(ResizableHashTable.MIN_SIZE):

m.put(i, 'foo')

self.assertEqual(ResizableHashTable.MIN_SIZE * 2, m.size)

self.assertEqual('foo', m.get(1))

self.assertEqual('foo', m.get(3))

self.assertEqual('foo', m.get(ResizableHashTable.MIN_SIZE - 1))

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