# Uncommon Big-O for Algorithm

Published on Wednesday, October 9, 2024

While the most common Big-O notations are well-known, there are several less frequent ones that can provide valuable insights into algorithm performance. These uncommon notations often represent algorithms with more complex characteristics or specialized applications.

By understanding these notations, you can gain a deeper appreciation for the diversity of algorithm performance and the challenges that can arise in algorithm design:

**Analyze algorithms that don’t fit the standard patterns.****Gain insights into the limitations and capabilities of different algorithms.****Make informed decisions about algorithm selection.**

It can also provide insights into the limitations and capabilities of different algorithms in various scenarios.

**Let’s start**

## Sublinear Time

$O(n^c)$ or

order n to the power of c.

Sublinear time algorithms are those that run in less than linear time. This means that their running time grows slower than the input size. While it might seem counterintuitive, sublinear time algorithms are possible in certain scenarios.

**Definition:** Algorithms that run in less than linear time.

**Examples:**

**Preprocessed data structures:**Searching in sorted arrays using binary search.**Approximate algorithms:**Algorithms that sacrifice accuracy for speed.**Specialized data structures:**Certain data structures, such as Bloom filters, can support operations in sublinear time.

## Factorial Time

$O(n!)$ or

order n factorial.

Factorial time algorithms are those whose running time grows extremely rapidly with the input size. The factorial function grows much faster than any polynomial or exponential function, making factorial time algorithms impractical for even moderately large inputs.

**Definition:** Algorithms whose running time grows extremely rapidly with the input size.

**Examples:**

**Brute-force algorithms:** Exploring all possible solutions to find the optimal one.

**Generating all permutations of a set.****Solving certain combinatorial problems:**Such as the traveling salesman problem or the knapsack problem.

## Exponential Time

$O(2^n)$ or

order 2 to the power of n.

Exponential time algorithms are those whose running time grows exponentially with the input size. This means that the time it takes to run the algorithm doubles for each additional unit of input. As a result, exponential time algorithms can become impractical even for relatively small input sizes.

**Definition:** Algorithms whose running time grows exponentially with the input size.

**Examples:**

**Brute-force algorithms:**Exploring all possible solutions.**Cryptographic algorithms:**Such as RSA.**Solving certain combinatorial problems:**Such as the subset sum problem or the Hamiltonian cycle problem.

## Polylogarithmic Time

$O(\log^k n)$ or

order log to the power of k.

Polylogarithmic time algorithms are those whose running time grows as a polynomial of logarithms of the input size. This means they’re efficient for large inputs.

**Definition:** Algorithms whose running time grows as a polynomial of logarithms of the input size.

**Examples:**

**Graph algorithms:**Dijkstra’s algorithm for finding the shortest path.**Numerical algorithms:**Strassen’s algorithm for matrix multiplication.**Computational geometry:**Finding the convex hull of a set of points.**Data structures:**Certain data structures, such as heaps and Fibonacci heaps, support operations in polylogarithmic time.

## Quasi-Linear Time

$O(n \log^k n)$ or

order n log to the power of k.

Quasi-linear time algorithms are those whose running time grows slightly faster than linear but slower than quadratic. They are often considered efficient for large inputs.

**Definition:** Algorithms whose running time grows slightly faster than linear but slower than quadratic.

**Examples:**

**Sorting algorithms:**Quicksort, heapsort.**Graph algorithms:**Kruskal’s algorithm for finding the minimum spanning tree.**Computational geometry:**Certain computational geometry problems.**Data structures:**Certain data structures, such as priority queues and range trees, support operations in quasi-linear time.

## Conclusion

By understanding these uncommon Big-O notations, you can:

- Analyze algorithms that don’t fit the standard patterns.
- Gain insights into the limitations and capabilities of different algorithms.
- Make informed decisions about algorithm selection.

**Remember:** These are just a few examples, and the specific notation used depends on the algorithm and problem. By mastering these uncommon notations, you can expand your knowledge of algorithm efficiency and make more informed decisions about algorithm selection.

For a more in-depth exploration of *common* Big-O notations, refer to our **comprehensive guide** here.