using System;
using System.Collections.Generic;
 
public static class RandomElementSelector
{
    public static IList<T> CollectAllowedElements<T>(IList<T> allElements, IList<T> excludedElements)
    {
        List<T> allowedElements = new List<T>();
        foreach (T element in allElements)
            if (!excludedElements.Contains(element))
                allowedElements.Add(element);
        return allowedElements;
    }
    
    public static T SelectRandomElement<T>(IList<T> allowedElements)
    {
        Random random = new Random();
        int randomIndex = random.Next(allowedElements.Count);
        return allowedElements[randomIndex];
    }
 
    public static T SelectRandomElement<T>(IList<T> allElements, IList<T> excludedElements)
    {
        IList<T> allowedElements = CollectAllowedElements(allElements, excludedElements);
        return SelectRandomElement(allowedElements);
    }
}
 
public class Test
{
    public static void Main()
    {
        const int N = 100;
        
        // Example #1
        int[] allNumbers = new int[N];
        for (int i = 0; i < allNumbers.Length; ++i)
            allNumbers[i] = i + 1;
        int[] excludedNumbers = { 5, 7, 17, 23 };
        Console.WriteLine(RandomElementSelector.SelectRandomElement(allNumbers, excludedNumbers));
        
        // Example #2
        List<string> allStrings = new List<string>();
        for (int i = 0; i < N; ++i)
            allStrings.Add("Item #" + (i + 1));
        string[] excludedStrings = { "Item #5", "Item #7", "Item #17", "Item #23" };
        Console.WriteLine(RandomElementSelector.SelectRandomElement(allStrings, excludedStrings));
        }
}