Checking if an Element Exists

Part of the Logic & Flow section of Coddy's C# journey — lesson 59 of 66.

The Contains(element) method checks if a specific element exists in the HashSet. It returns true if the element is found, and false otherwise.

Create an empty HashSet:

HashSet<string> fruits = new HashSet<string>();

Add some elements to the HashSet:

fruits.Add("Apple");
fruits.Add("Banana");

Check if an element exists:

bool hasApple = fruits.Contains("Apple");  // Returns true
bool hasOrange = fruits.Contains("Orange"); // Returns false

You can use the result in conditional statements:

if (fruits.Contains("Apple"))
{
    Console.WriteLine("Apple is in the set");
}

Challenge

Easy

Create a method named ElementExists that takes two arguments:

A HashSet of strings (set)
A string (element) to check

The method should check if the element exists in the set and return a string message:

If the element exists, return "The element 'X' exists in the set"
If the element doesn't exist, return "The element 'X' does not exist in the set"

Where 'X' is the actual element value being checked.

Cheat sheet

The Contains(element) method checks if a specific element exists in the HashSet. It returns true if the element is found, and false otherwise.

Create an empty HashSet:

HashSet<string> fruits = new HashSet<string>();

Add elements to the HashSet:

fruits.Add("Apple");
fruits.Add("Banana");

Check if an element exists:

bool hasApple = fruits.Contains("Apple");  // Returns true
bool hasOrange = fruits.Contains("Orange"); // Returns false

Use in conditional statements:

if (fruits.Contains("Apple"))
{
    Console.WriteLine("Apple is in the set");
}

Try it yourself

using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;

public class Program
{
    public static string ElementExists(HashSet<string> set, string element)
    {
        // Write your code here
        return "";
    }
    
    public static void Main()
    {
        // Read first line to check if it's JSON format
        string firstLine = Console.ReadLine();
        string elementToCheck = Console.ReadLine();
        HashSet<string> set = new HashSet<string>();
        
        // Check if input is in JSON array format
        if (firstLine != null && firstLine.StartsWith("[") && firstLine.EndsWith("]"))
        {
            try
            {
                // Extract content between square brackets
                string arrayContent = firstLine.Substring(1, firstLine.Length - 2);
                
                // Use regex to match all quoted strings
                MatchCollection matches = Regex.Matches(arrayContent, @"""([^""]*)""");
                
                foreach (Match match in matches)
                {
                    // Add the captured group (without quotes)
                    if (match.Groups.Count > 1)
                    {
                        set.Add(match.Groups[1].Value.Trim());
                    }
                }
                
                // Check if element is in JSON string format
                Match elementMatch = Regex.Match(elementToCheck, @"""([^""]*)""");
                if (elementMatch.Success && elementMatch.Groups.Count > 1)
                {
                    elementToCheck = elementMatch.Groups[1].Value;
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Error parsing JSON input: {ex.Message}");
                return;
            }
        }
        else
        {
            // Process traditional comma-separated input
            string[] elements = firstLine.Split(',');
            foreach (string element in elements)
            {
                set.Add(element.Trim());
            }
        }
        
        string result = ElementExists(set, elementToCheck);
        Console.WriteLine(result);
    }
}