How To Remove Duplicate Characters From String In C#?

In this article, we will examine different methods for eliminating duplicate characters from the specified string in C#.

There are numerous methods to erase duplicate characters from the string, but I will demonstrate three methods for doing so below.

Using LINQ
Using Simple Array
Using HashSet

Below are a few examples of inputs and Outputs.

Example 1

Input: GOOGLE
Result: GOLE

Example 2

Input: MOON
Result: MON

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Using LINQ

Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"Enter a String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name"><span class="token keyword keyword-var">var</span></span> str <span class="token operator">=</span> Console<span class="token punctuation">.</span><span class="token function">ReadLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token class-name"><span class="token keyword keyword-var">var</span></span> strArray <span class="token operator">=</span> str<span class="token punctuation">.</span><span class="token function">ToCharArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
                  <span class="token punctuation">.</span><span class="token function">Distinct</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
                  <span class="token punctuation">.</span><span class="token function">ToArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token class-name"><span class="token keyword keyword-string">string</span></span> result <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token constructor-invocation class-name"><span class="token keyword keyword-string">string</span></span><span class="token punctuation">(</span>strArray<span class="token punctuation">)</span><span class="token punctuation">;</span>
Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token interpolation-string"><span class="token string">$"</span><span class="token interpolation"><span class="token punctuation">{</span><span class="token expression language-csharp">result</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Console<span class="token punctuation">.</span><span class="token function">ReadLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Console.WriteLine("Enter a String");

var str = Console.ReadLine();

var strArray = str.ToCharArray()

.Distinct()

.ToArray();

string result = new string(strArray);

Console.WriteLine($"{result}");

Console.ReadLine();

Output

Using HashSet

We are going to implement the same functionality using HashSet.

Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"Enter a String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name"><span class="token keyword keyword-var">var</span></span> str <span class="token operator">=</span> Console<span class="token punctuation">.</span><span class="token function">ReadLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token class-name"><span class="token keyword keyword-var">var</span></span> strInput <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token constructor-invocation class-name">HashSet<span class="token punctuation">&lt;</span><span class="token keyword keyword-char">char</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span>str<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name"><span class="token keyword keyword-string">string</span></span> result <span class="token operator">=</span> <span class="token keyword keyword-new">new</span> <span class="token constructor-invocation class-name"><span class="token keyword keyword-string">string</span></span><span class="token punctuation">(</span>strInput<span class="token punctuation">.</span><span class="token function">ToArray</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token interpolation-string"><span class="token string">$"</span><span class="token interpolation"><span class="token punctuation">{</span><span class="token expression language-csharp">result</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Console<span class="token punctuation">.</span><span class="token function">ReadLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

var strInput = new HashSet<char>(str);

string result = new string(strInput.ToArray());

Let’s execute and see the output.

Output

Now we will try another simple array method to implement.

Using the Simple Array Method

Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token string">"Enter a String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name"><span class="token keyword keyword-var">var</span></span> str <span class="token operator">=</span> Console<span class="token punctuation">.</span><span class="token function">ReadLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name"><span class="token keyword keyword-string">string</span></span> result <span class="token operator">=</span> <span class="token keyword keyword-string">string</span><span class="token punctuation">.</span>Empty<span class="token punctuation">;</span>

<span class="token keyword keyword-for">for</span> <span class="token punctuation">(</span><span class="token class-name"><span class="token keyword keyword-int">int</span></span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> str<span class="token punctuation">.</span>Length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    <span class="token keyword keyword-if">if</span> <span class="token punctuation">(</span><span class="token operator">!</span>result<span class="token punctuation">.</span><span class="token function">Contains</span><span class="token punctuation">(</span>str<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token punctuation">{</span>
        result <span class="token operator">+=</span> str<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

Console<span class="token punctuation">.</span><span class="token function">WriteLine</span><span class="token punctuation">(</span><span class="token interpolation-string"><span class="token string">$"</span><span class="token interpolation"><span class="token punctuation">{</span><span class="token expression language-csharp">result</span><span class="token punctuation">}</span></span><span class="token string">"</span></span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Console<span class="token punctuation">.</span><span class="token function">ReadLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

for (int i = 0; i < str.Length; i++)

{

if (!result.Contains(str[i]))

{

result += str[i];

}

Output

We have learned three distinct methods to eliminate duplicate characters from the string. We hope you find this article enjoyable and useful.

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