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Marcin Jamro, PhD, DSc

How to find peaks in array?

C#  |  .NET  |  Algorithms

Let's imagine a task that you need to prepare the code finding peaks in an array. A peak is any element which value is higher than values of its neighbors. Of course, an array can contain many peaks and you should detect all of them. How can you solve this problem?

The solution is shown right below:

int[] GetPeaks(int[] a)
    List peaks = [];
    // Check whether the first element is a peak.
    if (a[0] >= a[1]) 
    // Check whether any element
    // (except the first and the last) is a peak.
    for (int i = 1; i < a.Length - 1; i++)
        if (a[i - 1] <= a[i] && a[i] >= a[i + 1]) 
    // Check whether the last element is a peak
    if (a[^1] >= a[^2])
    return [.. peaks];

You can check this code by the following lines:

int[] array = [10, 8, 7, 5, 2, 7, 4, 8, 2, 9];
Console.WriteLine($"Peaks are: {string.Join(", ", GetPeaks(array))}");

The results are shown as follows:

Peaks are: 10, 7, 8, 9

If you want to learn much more about arrays, as well as about other data structures, I encourage you to take a look at my book, namely the Second Edition of C# Data Structures and Algorithms, published by Packt Publishing in 2024. You can buy it here.

The content, including any part of code, is presented without warranty, either express or implied. The author cannot be held liable for any damages caused or alleged to have been caused directly or indirectly by any content shown on this website.

Hello, I am Marcin

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I am an author of a few books and numerous publications, also in high-quality international scientific journals.

If you want to learn data structures and algorithms in the context of C#, let's take a look at my newest book. It is the second edition of C# Data Structures and Algorithms. You can buy it here.


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