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How to Implement a Hash Table from Scratch in python?

It might be rewarding to implement a hash table from scratch in your preferred programming language
in order to better comprehend data structures and algorithms. Here is how to make a simple hash table

  • Step 1: Define Your Hash Table Class:

Create a class for your hash table first. The data members of this class should
have an array to store the buckets, a size variable, and methods for adding, removing, and retrieving
key-value pairs.

class HashTable:
 def __init__(self, size):
 self.size = size
 self.table = [None] * size
  • Step 2: Choose a Hash Function:

Choose a hashing operation that converts a key into an index in your array. A straightforward hash function involves adding the ASCII values of the key’s characters, followed by multiplying the result by the size of the array.

def hash_function(self, key):
 key_sum = sum(ord(char) for char in key)
 return key_sum % self.size
  • Step 3: Implement Insertion:

Making a way to add key-value pairs to your hash table is necessary. Find the index where the key-value pair should be placed by using the hash function. Utilize chaining (linked lists in each bucket) or open addressing to handle collisions (when several keys hash to the same index).

def insert(self, key, value):
 index = self.hash_function(key)
 if self.table[index] is None:
     self.table[index] = []
 self.table[index].append((key, value))
  • Step 4: Implement Retrieval:

Implement a method to retrieve values based on keys. Again, use the hash function to find the index, and then search for the key in the corresponding bucket.

def get(self, key):
 index = self.hash_function(key)
 if self.table[index] is not None:
 for k, v in self.table[index]:
    if k == key:
       return v
 return None # Key not found#
  • Step 5: Implement Deletion:

To delete key-value pairs depending on keys, develop a method. Use the hash function to get the index in a manner similar to retrieval, and then take the key-value pair out of the bucket.

def delete(self, key):
 index = self.hash_function(key)
 if self.table[index] is not None:
 for i, (k, v) in enumerate(self.table[index]):
    if k == key:
       del self.table[index][i]
       return v
  •  Step 6: Test Your Hash Table:

Write test cases to ensure that your hash table works as expected. Test insertion, retrieval, and deletion for different key-value pairs and edge cases.

  • Step 7: Handling Resizing:

To make your hash table more efficient, consider implementing resizing logic. When the number of elements in the hash table exceeds a certain threshold, double the size of the array and rehash all elements.

  • Step 8: Additional Considerations:

You may want to add error handling for invalid input, implement other hash functions for better distribution, and optimize your code for better performance.

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