Design HashSet in Python

Suppose we want to design a HashSet data structure without using any built-in hash table libraries. There will be different functions like −

• add(x) − Inserts a value x into the HashSet.
• contains(x) − Checks whether the value x is present in the HashSet or not.
• remove(x) − Removes x from the HashSet. In case the value does not exist in the HashSet, do nothing.

So, to test it Initialize the hash set, then call add(1), add(3), contains(1), contains(2), add(2), contains(2), remove(2), contains(2)., then the output will be true (1 is present), false (2 is not present), true (2 is present), false (2 is not present) respectively.

To solve this, we will follow these steps −

• Define one data structure called Bucket, Initialize it like below
• bucket := a new list
• Define a function update(). This will take key
• found := False
• for each index i and key k in bucket, do
  • if key is same as k, then
    • bucket[i]:= key
    • found:= True
    • come out from the loop
  • if found false, then
    • insert key at the end of bucket
• Define a function get() . This will take key
  • for each k in bucket, do
    • if k is same as key, then
      • return True
    • return False
• Define a function remove(). This will take key
  • for each index i and key k in bucket, do
    • if key is same as k, then
      • delete bucket[i]
• Now create custom hashSet. There will be few methods as follows
• Initialize this as follows −
• key_space := 2096
• hash_table:= a list of bucket type object of size key_space
• Define a function add(). This will take key
  • hash_key:= key mod key_space
  • call update(key) of hash_table[hash_key]
• Define a function remove(). This will take key
  • hash_key:= keymodkey_space
  • delete key from hash_table[hash_key]
• Define a function contains(). This will take key
  • hash_key:= keymodkey_space
  • return get(key) of hash_table[hash_key]

Let us see the following implementation to get better understanding −

Example

 Live Demo

class Bucket:
   def __init__(self):
      self.bucket=[]
   def update(self, key):
      found=False
      for i,k in enumerate(self.bucket):
         if key==k:
            self.bucket[i]=key
            found=True
            break
      if not found:
         self.bucket.append(key)
   def get(self, key):
      for k in self.bucket:
         if k==key:
            return True
      return False
   def remove(self, key):
      for i,k in enumerate(self.bucket):
         if key==k:
            del self.bucket[i]
class MyHashSet:
   def __init__(self):
      self.key_space = 2096
      self.hash_table=[Bucket() for i in range(self.key_space)]
   def add(self, key):
      hash_key=key%self.key_space
      self.hash_table[hash_key].update(key)
   def remove(self, key):
      hash_key=key%self.key_space
      self.hash_table[hash_key].remove(key)
   def contains(self, key):
      hash_key=key%self.key_space
      return self.hash_table[hash_key].get(key)
ob = MyHashSet()
ob.add(1)
ob.add(3)
print(ob.contains(1))
print(ob.contains(2))
ob.add(2)
print(ob.contains(2))
ob.remove(2)
print(ob.contains(2))

Input

ob = MyHashSet()
ob.add(1)
ob.add(3)
print(ob.contains(1))
print(ob.contains(2))
ob.add(2)
print(ob.contains(2))
ob.remove(2)
print(ob.contains(2))

Output

True
False
True
False

Arnab Chakraborty

Updated on: 04-Jul-2020

3K+ Views

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