Describe how a hash table works.

Explanation:
A hash table is a data structure that provides a way to store and retrieve data efficiently through key-value pairs. It uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found. Hash tables are commonly used to implement associative arrays or mappings. The main advantage of a hash table is its ability to perform insertions, deletions, and lookups in average constant time, O(1), given a good hash function and low collision rate.

Key Talking Points:

• Data Structure: Stores key-value pairs.
• Hash Function: Converts keys into array indices.
• Efficiency: Average case time complexity for insert, delete, and lookup is O(1).
• Collisions: Occur when two keys hash to the same index; handled by methods like chaining or open addressing.
• Applications: Often used in databases, caches, and associative arrays.

NOTES:

Reference Table:

Pseudocode:

initialize hash_table with size n

function put(key, value):
    index = hash_function(key) % n
    if hash_table[index] is empty:
        hash_table[index] = [(key, value)]
    else:
        for each element in hash_table[index]:
            if element.key == key:
                update element.value to value
                return
        add (key, value) to hash_table[index]

function get(key):
    index = hash_function(key) % n
    if hash_table[index] is not empty:
        for each element in hash_table[index]:
            if element.key == key:
                return element.value
    return null

Follow-Up Questions and Answers:

1. Question: What is a hash collision and how can it be handled?

   • Answer: A hash collision occurs when two keys hash to the same index in a hash table. It can be handled using techniques like chaining, where each bucket is a linked list of entries, or open addressing, where a probing sequence is used to find the next available slot.

2. Question: Can you explain some real-world scenarios where hash tables are used?

   • Answer: Hash tables are used in scenarios like database indexing, implementing caches, and storing configurations or settings where quick access to key-value pairs is crucial.

3. Question: What are the limitations of hash tables?

   • Answer: Hash tables can suffer from poor performance if the hash function results in too many collisions. They also do not maintain order of elements and can be inefficient for operations requiring ordered data, like finding the minimum or maximum values. Additionally, resizing a hash table can be costly.