Data Structures and Algorithms

# How to Create Hashing Table Using Open Addressing?

## What is a Hash Table?

Basically, a hash table is a data structure that stores keys and their associated values, and allows fast lookup, insertion, and deletion of key-value pairs. Open addressing is one technique for implementing a hash table, where collisions are resolved by finding an alternative empty slot in the table.

The following steps show how to create a hash table using open addressing.

1. Choose a hash function: A hash function is a function that maps a key to an index in the hash table. The hash function should be designed to distribute the keys evenly across the hash table.
2. Create an array to store the key-value pairs: The size of the array should be chosen based on the expected number of key-value pairs that will be stored in the table.
3. Initialize the array: Set all the elements in the array to a special value, such as NULL, to indicate that they are empty.
4. Insert key-value pairs: To insert a key-value pair into the hash table, compute the hash value of the key using the hash function. If the slot at the computed index is empty, insert the key-value pair in that slot. If the slot is already occupied by another key-value pair, use open addressing to find the next available slot. One common approach is linear probing, which involves checking the next slot in the array until an empty slot is found.
5. Lookup key-value pairs: To lookup a key in the hash table, compute the hash value of the key using the hash function. If the slot at the computed index contains the key, return the associated value. If the slot is empty or contains a different key, use open addressing to search for the key in the next slots of the array until the key is found or an empty slot is reached.
6. Delete key-value pairs: To delete a key-value pair from the hash table, lookup the key using the same process as in step 5. If the key is found, delete the key-value pair by marking the slot as empty. If the key is not found, the operation has no effect.

## Conclusion

In conclusion, by using open addressing, a hash table can handle collisions without needing to use separate chaining or other techniques that require additional memory overhead. However, the performance of open addressing can degrade as the hash table becomes more densely filled, and it may be necessary to periodically rehash the table to maintain good performance.

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