Is there any HashSet implementation in Python? I know HashTable can be represented using dictionaries, but how do we represent HashSet implementation.
I am NOT looking for a data structure with the same methods as HashSets but rather someone with a CONSTANT lookup time, or the order of O(1);
Also, I want to know if the lookup time in a Python Dictionary is constant aka O(1)
I think the HashSet implementation you are looking is set(). This answer may help you: What's the difference between HashSet and Set?
And yes, the average time complexity for python dictionary O(1). You may read on why we use the term: "Average time complexity": Time complexity of accessing a Python dict
I guess this is what you want. You may define a hash function yourself, like what I did in HashSet or just use the built-in hash() function in Python.
class HashSet:
CONST = 2 ** 61 - 1
def __init__(self, size = 10_000):
self.size = size * 2
self.contents = [None] * self.size
def hash(self, x):
return x % CONST
def put(self, key):
idx = self.hash(key) % self.size
arr = self.contents[idx]
if arr is None:
self.contents[idx] = [key]
elif key not in arr:
arr.append(key)
return None
def get(self, key):
idx = self.hash(key) % self.size
arr = self.contents[idx]
if arr is None or key not in arr:
return False
return True
myset = HashSet()
myset.put(123)
myset.put(145)
myset.put(138)
res = myset.get(145)
print(res)
res = myset.get(10)
print(res)
class HashMap:
def __init__(self, size = 10_000):
self.size = size * 2
self.contents = [None] * self.size
class __Pair:
def __init__(self, key, value):
self.key = key
self.value = value
def find(self, arr, key):
for pair in arr:
if pair.key == key:
return pair
return None
def put(self, key, value):
idx = hash(key) % self.size
pair = self.__Pair(key, value)
arr = self.contents[idx]
if arr is None:
self.contents[idx] = [pair,]
return None
t = self.find(arr, key)
if t != None:
t.value = value
else:
arr.append(pair)
def get(self, key):
idx = hash(key) % self.size
arr = self.contents[idx]
if arr == None:
raise KeyError(f'{key} is not a valid key')
t = self.find(arr, key)
if t == None:
raise KeyError(f'{key} is not a valid key')
return t.value
mymap = HashMap()
mymap.put('abc', [123,456])
mymap.put('def', [456,789])
res = mymap.get('abc')
print(res)
res = mymap.get('def')
print(res)
res = mymap.get('defx')
print(res)
@Ayush Gupta, I have implemented the HashSet. Please do have a look at it. Comment for any feedback.
class MyHashSet:
def __init__(self):
self.l = []
def add(self, key: int) -> None:
if key not in self.l:
self.l.append(key)
def remove(self, key: int) -> None:
if key in self.l:
self.l.remove(key)
def contains(self, key: int) -> bool:
return key in self.l
# Your MyHashSet object will be instantiated and called as such:
obj = MyHashSet()
obj.add(key)
obj.remove(key)
param_3 = obj.contains(key)
item in list is O(n).
set()? And for complexity, read this: wiki.python.org/moin/TimeComplexitysetis HashSets and for your "also", yes.set()have ahasmethod to check whether a given value exists in the set? I sawx in sin the docs, but I'm not sure if it can be used to inifor only in afor. I'm new to python so haven't really usedset()beforeset~HashSetanddictisHashTableif x in set()is the Pythonic (the "recommended") way of testing belonging (if x in dict()checks ifxis among the dictionarykeys). Take a look to docs.python.org/3/reference/datamodel.html#object.__hash__ (there's a lot of interesting information and links to other juicy parts of the documentation in that page)