mirror of
https://github.com/TheAlgorithms/Python.git
synced 2025-07-07 19:46:30 +08:00
Add hashmap implementation (#7967)
This commit is contained in:
162
data_structures/hashing/hash_map.py
Normal file
162
data_structures/hashing/hash_map.py
Normal file
@ -0,0 +1,162 @@
|
||||
"""
|
||||
Hash map with open addressing.
|
||||
|
||||
https://en.wikipedia.org/wiki/Hash_table
|
||||
|
||||
Another hash map implementation, with a good explanation.
|
||||
Modern Dictionaries by Raymond Hettinger
|
||||
https://www.youtube.com/watch?v=p33CVV29OG8
|
||||
"""
|
||||
from collections.abc import Iterator, MutableMapping
|
||||
from dataclasses import dataclass
|
||||
from typing import Generic, TypeVar
|
||||
|
||||
KEY = TypeVar("KEY")
|
||||
VAL = TypeVar("VAL")
|
||||
|
||||
|
||||
@dataclass(frozen=True, slots=True)
|
||||
class _Item(Generic[KEY, VAL]):
|
||||
key: KEY
|
||||
val: VAL
|
||||
|
||||
|
||||
class _DeletedItem(_Item):
|
||||
def __init__(self) -> None:
|
||||
super().__init__(None, None)
|
||||
|
||||
def __bool__(self) -> bool:
|
||||
return False
|
||||
|
||||
|
||||
_deleted = _DeletedItem()
|
||||
|
||||
|
||||
class HashMap(MutableMapping[KEY, VAL]):
|
||||
"""
|
||||
Hash map with open addressing.
|
||||
"""
|
||||
|
||||
def __init__(
|
||||
self, initial_block_size: int = 8, capacity_factor: float = 0.75
|
||||
) -> None:
|
||||
self._initial_block_size = initial_block_size
|
||||
self._buckets: list[_Item | None] = [None] * initial_block_size
|
||||
assert 0.0 < capacity_factor < 1.0
|
||||
self._capacity_factor = capacity_factor
|
||||
self._len = 0
|
||||
|
||||
def _get_bucket_index(self, key: KEY) -> int:
|
||||
return hash(key) % len(self._buckets)
|
||||
|
||||
def _get_next_ind(self, ind: int) -> int:
|
||||
"""
|
||||
Get next index.
|
||||
|
||||
Implements linear open addressing.
|
||||
"""
|
||||
return (ind + 1) % len(self._buckets)
|
||||
|
||||
def _try_set(self, ind: int, key: KEY, val: VAL) -> bool:
|
||||
"""
|
||||
Try to add value to the bucket.
|
||||
|
||||
If bucket is empty or key is the same, does insert and return True.
|
||||
|
||||
If bucket has another key or deleted placeholder,
|
||||
that means that we need to check next bucket.
|
||||
"""
|
||||
stored = self._buckets[ind]
|
||||
if not stored:
|
||||
self._buckets[ind] = _Item(key, val)
|
||||
self._len += 1
|
||||
return True
|
||||
elif stored.key == key:
|
||||
self._buckets[ind] = _Item(key, val)
|
||||
return True
|
||||
else:
|
||||
return False
|
||||
|
||||
def _is_full(self) -> bool:
|
||||
"""
|
||||
Return true if we have reached safe capacity.
|
||||
|
||||
So we need to increase the number of buckets to avoid collisions.
|
||||
"""
|
||||
limit = len(self._buckets) * self._capacity_factor
|
||||
return len(self) >= int(limit)
|
||||
|
||||
def _is_sparse(self) -> bool:
|
||||
"""Return true if we need twice fewer buckets when we have now."""
|
||||
if len(self._buckets) <= self._initial_block_size:
|
||||
return False
|
||||
limit = len(self._buckets) * self._capacity_factor / 2
|
||||
return len(self) < limit
|
||||
|
||||
def _resize(self, new_size: int) -> None:
|
||||
old_buckets = self._buckets
|
||||
self._buckets = [None] * new_size
|
||||
self._len = 0
|
||||
for item in old_buckets:
|
||||
if item:
|
||||
self._add_item(item.key, item.val)
|
||||
|
||||
def _size_up(self) -> None:
|
||||
self._resize(len(self._buckets) * 2)
|
||||
|
||||
def _size_down(self) -> None:
|
||||
self._resize(len(self._buckets) // 2)
|
||||
|
||||
def _iterate_buckets(self, key: KEY) -> Iterator[int]:
|
||||
ind = self._get_bucket_index(key)
|
||||
for _ in range(len(self._buckets)):
|
||||
yield ind
|
||||
ind = self._get_next_ind(ind)
|
||||
|
||||
def _add_item(self, key: KEY, val: VAL) -> None:
|
||||
for ind in self._iterate_buckets(key):
|
||||
if self._try_set(ind, key, val):
|
||||
break
|
||||
|
||||
def __setitem__(self, key: KEY, val: VAL) -> None:
|
||||
if self._is_full():
|
||||
self._size_up()
|
||||
|
||||
self._add_item(key, val)
|
||||
|
||||
def __delitem__(self, key: KEY) -> None:
|
||||
for ind in self._iterate_buckets(key):
|
||||
item = self._buckets[ind]
|
||||
if item is None:
|
||||
raise KeyError(key)
|
||||
if item is _deleted:
|
||||
continue
|
||||
if item.key == key:
|
||||
self._buckets[ind] = _deleted
|
||||
self._len -= 1
|
||||
break
|
||||
if self._is_sparse():
|
||||
self._size_down()
|
||||
|
||||
def __getitem__(self, key: KEY) -> VAL:
|
||||
for ind in self._iterate_buckets(key):
|
||||
item = self._buckets[ind]
|
||||
if item is None:
|
||||
break
|
||||
if item is _deleted:
|
||||
continue
|
||||
if item.key == key:
|
||||
return item.val
|
||||
raise KeyError(key)
|
||||
|
||||
def __len__(self) -> int:
|
||||
return self._len
|
||||
|
||||
def __iter__(self) -> Iterator[KEY]:
|
||||
yield from (item.key for item in self._buckets if item)
|
||||
|
||||
def __repr__(self) -> str:
|
||||
val_string = " ,".join(
|
||||
f"{item.key}: {item.val}" for item in self._buckets if item
|
||||
)
|
||||
return f"HashMap({val_string})"
|
Reference in New Issue
Block a user