Explain what a hash table data structure is and how it works

A hash table is a data structure that stores key-value pairs and provides very fast access to data by key. It works using a hash function that transforms the key into an array index where the value is stored.

Working principle:

1. When adding a key-value pair, the key is processed through the hash function, which returns an index.
2. The value is stored in the array at this index.
3. When searching for a key, the hash function again calculates the index, and the value is quickly retrieved.

To avoid collisions (when different keys produce the same index), methods such as:

• chaining (storing multiple elements in one cell as a list)
• open addressing (searching for the next free cell)

In C#, an example of using a dictionary (Dictionary), which is implemented based on a hash table:

var dict = new Dictionary<string, int>();
dict["apple"] = 5;
int value = dict["apple"]; // value == 5

Hash tables provide an average complexity of O(1) for insert, delete, and search operations.