# Common Big-O for Algorithms

Published on Friday, August 11, 2023 - Updated 3 weeks ago

**Imagine you’re planning a party.** You’ve got a guest list, decorations, and a menu. Now, imagine adding more and more guests. How much longer would it take you to prepare?

This is essentially what Big-O notation is all about. It’s a way to measure how an algorithm’s performance scales as the input size grows. In simpler terms, it helps us understand how quickly an algorithm will slow down as the data it processes gets larger.

**Why is Big-O important?** Think of it like choosing the right car for a road trip. If you’re going a short distance, a fuel-efficient car might be fine. But for a long journey, you’d want something more powerful. Similarly, for small datasets, an algorithm with a higher Big-O might be acceptable. But as the data grows, a lower Big-O becomes crucial to prevent performance bottlenecks.

The most common time complexities, which will be covered here, are $O(1)$, $O(\log n)$, $O(n)$, $O(n \log n)$ and $O(n^2)$. We will follow this order as well.

**Let’s break down the most common Big-O notations.**

## Constant Time

$O(1)$ or

order 1.

The concept of constant time algorithms dates back to ancient Greece with the Euclidean algorithm. As computers became more prevalent, computer scientists formalized the concept of time complexity. Pioneers like Donald Knuth contributed to developing mathematical tools for analyzing algorithm efficiency.

Today, constant time algorithms are essential for efficient data structures and algorithms, such as hash tables. They are also crucial in real-time systems where operations must be performed within strict time constraints.

**Think of it as a fixed speed limit.** No matter how much data you throw at it, the algorithm’s performance stays the same.

**Example:** Accessing an element in an array by its index.

**Real-world analogy:** Imagine a vending machine. No matter how many times you press the buttons, the time it takes to dispense your item remains constant.

## Logarithmic Time

$O(\log n)$ or

order n log n.

The concept of logarithmic time algorithms emerged alongside the development of efficient searching and sorting techniques. Binary search, a classic example of a logarithmic time algorithm, was formalized in the mid-20th century.

As computers became more powerful and data sets grew larger, logarithmic time algorithms became increasingly important. They are essential for efficient searching, sorting, and computational tasks where the input size can vary significantly.

**Imagine halving the problem repeatedly.** As the data doubles, the algorithm’s time increases only slightly.

**Example:** Binary search.

**Real-world analogy:** Think of searching for a word in a dictionary. You don’t start at the beginning and read every word. Instead, you open the dictionary to the middle, check if the word is there, and then decide to search the left or right half. This process of halving the search space is logarithmic.

## Linear Time

$O(n)$ or

order n.

Linear time algorithms are among the most fundamental and widely used in computer science. Their history can be traced back to the early days of computing, when simple algorithms for tasks like searching and sorting were developed.

As computers became more powerful and data sets grew larger, linear time algorithms remained essential for many applications. While they may not be the most efficient for extremely large data sets, they often provide a good balance of speed and simplicity.

**Think of a directly proportional relationship.** As the data doubles, the algorithm’s time doubles.

**Example:** Iterating through an array once.

**Real-world analogy:** Imagine counting the number of people in a line. For each person you count, the time it takes increases linearly.

## Linearithmic Time

$O(n \log n)$ or

order n log n.

Linearithmic time algorithms, often associated with divide-and-conquer strategies, emerged in the mid-20th century. Merge sort, a classic example of a linearithmic time algorithm, was developed by John von Neumann.

As computers became more powerful and data sets grew larger, linearithmic time algorithms became increasingly important for sorting and other computational tasks. They offer a balance of efficiency and simplicity, making them a popular choice in many applications.

**A combination of linear and logarithmic.** The algorithm’s time grows slightly faster than linearly but slower than quadratically.

**Example:** Merge sort.

**Real-world analogy:** Imagine sorting a deck of cards. You start by dividing the deck in half, then sort each half, and finally merge the sorted halves. This process involves both linear (dividing the deck) and logarithmic (sorting each half) steps.

## Quadratic Time

$O(n^2)$ or

order n squared.

Quadratic time algorithms, while often less efficient than their linear or logarithmic counterparts, have a long history in computer science. Simple sorting algorithms like bubble sort and insertion sort, which have quadratic time complexity, were among the first algorithms developed for computers.

While quadratic time algorithms may not be ideal for large data sets, they can still be useful in certain scenarios, especially when simplicity and ease of implementation are more important than performance. As computers have become more powerful, the practical limitations of quadratic time algorithms have become less severe, allowing them to be used in a wider range of applications.

**Imagine a growing square.** As the data doubles, the algorithm’s time quadruples.

**Example:** Nested loops iterating over the same data.

**Real-world analogy:** Imagine comparing every person in a room to every other person to find a match. As the number of people doubles, the number of comparisons increases quadratically.

## Conclusion

**Big-O is a fundamental concept in computer science that provides a valuable tool for analyzing and optimizing algorithms.** By understanding Big-O, you can make informed decisions about algorithm selection, predict scalability, and write more efficient and maintainable code. So, the next time you’re faced with a performance challenge, remember Big-O and choose the right algorithm for the job!

**Key takeaways:**

- Big-O notation is a powerful tool for analyzing algorithm efficiency.
- Understanding Big-O notation is essential for writing efficient and scalable code.
- There are many different Big-O notations, each with its own characteristics.
- Choosing the right algorithm for a given task depends on the specific requirements and constraints.

For an exploration of *uncommon* Big-O notations, refer to our **extended guide** here.