Welcome, fellow newbies, let’s talk about hash tables! If you’re starting to learn about algorithms and data structures, hash tables are a fundamental topic that you’ll bump into. Having a good understanding of it can even come in handy in interviews or building your first projects.

What Are Hash Tables? 🤔

Hash tables are data structures that allow you to store and retrieve values based on a given key. The magic sauce behind its efficiency lies in its hashing function, which takes in a key and outputs a specific index or bucket, where the key-value pair will be stored.

When you want to search for a value in a hash table, you provide the key, which then undergoes the same hashing function, and the index it returns will be the location of the value you are looking for.

Basically, you just create a relationship between the values and keys using some unique computation to quickly access them later.

A table with keys and values connected by arrows

Why Use Hash Tables? 🤷

Hash tables are a very efficient way to store and access data. Lookup time is minimal and average, even if you have millions of elements to search through.

Using a hash function allows you to get a constant time access no matter the number of elements you store. Storing and retrieving values in a hash table has a worst-case complexity of O(1).

Hash tables also provide an easy-to-use API to manipulate its contents. These benefits make them an excellent choice when you need to store and retrieve large amounts of data quickly.

Two arrows, one pointing upwards and one downwards, meeting at a middle point, represent the speed and efficiency of hash tables

How Do Hash Tables Work? ⚙️

Hash tables use arrays to store key-value pairs. A hash function takes the key and calculates the index in the array where the value is to be stored. Instead of using the key as the index directly, the hash function applies a calculation on it to return a smaller range that represents the index.

If imagine an array with 100 buckets, you can apply the modulo operation with the hash code to have a smaller equal or less than 100 value to use as the index. You can use any calculation that produces a fixed number of outcomes to make sure not to overlap entries.

Typically, to avoid collisions, hash tables use a linked list to chain values that end up hashed into the same bucket. In case you have two values of different keys that get a hash that returns the same index, you create a linked list that has the different values for that index in the list order.

Keep in mind that the efficiency of the hash table largely depends on the quality of the hash function you use.

A bucket with two linked values, with arrows showing they are chained together

Conclusion 🎉

In summary, hash tables are a popular way to implement key-value data structures. Their speed and efficiency make them popular in computer science, and they are common in real-world applications where accessing data fast is a must.

Thanks for your time, and I hope you learned something new and delightful!

A happy computer with hash tables coming out of it, surrounded by smiling clouds