What Is Big O Notation in Data Structure Geeksforgeeks?


Scott Campbell

Big O notation is a concept that is crucial to understand in the field of data structure and algorithm analysis. It is used to describe the efficiency or complexity of an algorithm, specifically how its running time or space requirements grow as the input size increases. In this tutorial, we will delve into the details of Big O notation and explore its significance in analyzing algorithms.

What is Big O Notation?

Big O notation is a mathematical representation used to describe the upper bound or worst-case scenario of an algorithm’s time complexity. It provides a way to estimate how an algorithm’s performance scales with increasing input size.

The “O” in Big O stands for “order of,” indicating the order of magnitude or growth rate of an algorithm’s time complexity. It allows us to compare algorithms and determine which one is more efficient based on their respective growth rates.

Why do we need Big O Notation?

Understanding an algorithm’s efficiency is essential when dealing with large-scale problems or huge datasets. By using Big O notation, we can assess how an algorithm will perform as the input size grows exponentially.

By analyzing time complexities, we can identify algorithms that are more scalable and efficient compared to others. This knowledge enables us to make informed decisions when choosing algorithms for solving specific problems.

How does Big O Notation work?

In Big O notation, we express the worst-case time complexity of an algorithm as a function of the input size n. The function represents the number of operations required by the algorithm relative to n. However, Big O notation ignores constant factors and lower-order terms, focusing solely on the dominant term that has the most significant impact on performance.

Let’s look at some common examples:

  • O(1) – Constant Time: Algorithms with constant time complexity execute in the same amount of time, regardless of the input size. For example, accessing an element in an array by index takes constant time since it does not depend on the array’s size.
  • O(log n) – Logarithmic Time: Algorithms with logarithmic complexity divide the input into smaller parts in each step.

    Binary search is an example of a logarithmic time algorithm, as it halves the search space at each iteration.

  • O(n) – Linear Time: Algorithms with linear complexity have a running time that grows linearly with the input size. For instance, iterating through all elements in an array requires a number of operations proportional to its size.
  • O(n^2) – Quadratic Time: Algorithms with quadratic complexity have nested loops resulting in exponential growth. Sorting algorithms like bubble sort and selection sort fall into this category.


Big O notation is a powerful tool for understanding and comparing algorithmic efficiency. By analyzing an algorithm’s worst-case time complexity, we can make informed decisions about which algorithms are best suited for specific scenarios.

Remember, Big O notation provides an upper bound on an algorithm’s performance; it does not necessarily represent its actual running time in every case. However, by focusing on worst-case scenarios and ignoring lower-order terms and constants, Big O notation allows us to gain valuable insights into an algorithm’s scalability.

So next time you come across Big O notation while studying data structures and algorithms, embrace it as a valuable tool to assess efficiency and choose the most optimal solutions for your programming problems!

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