How to Remove Duplicate Characters from a String in C#: A Beginner's Guide

In this article, we’ll learn how to remove duplicate characters from a String in C# using multiple examples.

Table of Contents

1 Understanding the Problem
2 Method 1: Remove duplicate characters using a HashSet
3 Method 2: Remove duplicate characters from a String Using LINQ
4 Method 3: Using String.Contains Method
- 4.1 Related

Understanding the Problem

Before diving into the code, let’s make sure we understand the problem. Removing duplicate characters means eliminating any characters that appear more than once in a given string.

For example, in the string “programming,” Our goal is to eliminate duplicate characters and transform the string into “progamin“.

Method 1: Remove duplicate characters using a HashSet

One of the most efficient ways to remove duplicate characters from a String is by using a HashSet. The HashSet is a collection that does not allow duplicate elements.

Here is a simple C# code snippet demonstrating this approach:

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        string input = "programming";
        string result = RemoveDuplicatesHashSet(input);

        Console.WriteLine("Original String: " + input);
        Console.WriteLine("String without Duplicates: " + result);
    }

    static string RemoveDuplicatesHashSet(string input)
    {
    // Creating a HashSet automatically removes duplicates.
        HashSet<char> uniqueChars = new HashSet<char>(input);

        string result = "";
      // Adding each unique character to the result using "foreach" loop.
        foreach (char c in uniqueChars)
        {
                result += c;
        }

        return result;
    }
}

Output:

Original String: programming
String without Duplicates: progamin

Method 2: Remove duplicate characters from a String Using LINQ

For those who prefer a more concise solution, LINQ provides an elegant way to remove duplicate characters from a string. Make sure to include the using System.Linq; directive in your code.

Here is an example:

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        string input = "programming";
        string result = RemoveDuplicatesLinq(input);

        Console.WriteLine("Original String: " + input);
        Console.WriteLine("String without Duplicates: " + result);
    }

    static string RemoveDuplicatesLinq(string input)
    {

       // We use the Distinct() method to get unique characters
        // Then, we convert the result back to a string using ToArray() and the new string constructor

        string result = new string(input.Distinct().ToArray());
        return result;
    }
}

Output:

Original String: programming
String without Duplicates: progamin

Method 3: Using String.Contains Method

Using the String.Contains method is another approach to remove duplicate characters from a string in C#.

Below is a simple program demonstrating this method:

using System;

class Program
{
    static void Main()
    {
        string input = "Google";
        string result = RemoveDuplicatesContains(input);

        Console.WriteLine("Original String: " + input);
        Console.WriteLine("String without Duplicates: " + result);
    }

    static string RemoveDuplicatesContains(string input)
    {
        string result = "";

        foreach (char c in input)
        {
            if (!result.Contains(c))
            {
                result += c;
            }
        }

        return result;
    }
}

Output:

Original String: Google
String without Duplicates: Gogle

Code Explanation:

We use a foreach loop to iterate through each character in the input string.
The String.Contains method is used to check if the character is already present in the result string.
If the character is not found in the result string, it is appended to the result.

While this approach is straightforward to remove duplicate characters from a string in C#, it’s worth noting that it may not be as efficient as the HashSet or LINQ methods, especially for large strings as the String.Contains method has a linear time complexity.

However, for smaller strings or simple use cases, it provides a readable and easy-to-understand solution.

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Author
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Shekh Ali

Meet Sheikh Ali, a skilled Software engineer and passionate a blogger. He enjoys sharing his expertise in C#, Java, SQL, Design Patterns, and other related topics through his writing. When he's not coding, Sheikh Ali can often indulge in his passions for reading books and fitness training.

Understanding the Problem

Method 1: Remove duplicate characters using a HashSet

Method 2: Remove duplicate characters from a String Using LINQ

Method 3: Using String.Contains Method

Related