/*
* ============================================================
* Title: Select N Random Elements from a List<T>
* ============================================================
*
* Description:
* This program demonstrates how to randomly select N unique
* elements from a List<T> in C#.
*
* Best Practices Used:
* - Generic method (works with any type)
* - Input validation
* - Does not modify the original list
* - Fisher-Yates shuffle for unbiased randomization
* - Clear comments and documentation
* - Exception handling
*
* ============================================================
*/
using System;
using System.Collections.Generic;
namespace RandomElementSelection
{
class Program
{
static void Main()
{
// Sample data
List<string> fruits = new List<string>
{
"Apple",
"Banana",
"Orange",
"Mango",
"Grape",
"Pineapple",
"Peach",
"Cherry",
"Kiwi",
"Strawberry"
};
int numberToSelect = 3;
try
{
// Select random elements
List<string> selectedItems =
GetRandomElements(fruits, numberToSelect);
Console.WriteLine("Original List:");
foreach (string fruit in fruits) {
Console.WriteLine($" {fruit}");
}
Console.WriteLine();
Console.WriteLine($"Randomly Selected {numberToSelect} Items:");
foreach (string item in selectedItems) {
Console.WriteLine($" {item}");
}
}
catch (Exception ex)
{
Console.WriteLine("Error: " + ex.Message);
}
}
/// <summary>
/// Returns N unique random elements from a list.
/// </summary>
/// <typeparam name="T">The type stored in the list.</typeparam>
/// <param name="source">Source list.</param>
/// <param name="count">Number of elements to select.</param>
/// <returns>A list containing randomly selected elements.</returns>
private static List<T> GetRandomElements<T>(
List<T> source,
int count)
{
// Validate input
if (source == null) {
throw new ArgumentNullException(nameof(source));
}
if (count < 0 || count > source.Count) {
throw new ArgumentOutOfRangeException(
nameof(count),
"Count must be between 0 and the number of items in the list.");
}
// Create a copy so the original list remains unchanged
List<T> shuffled = new List<T>(source);
// Create a Random instance
Random random = new Random();
// Fisher-Yates Shuffle
for (int i = shuffled.Count - 1; i > 0; i--) {
int j = random.Next(i + 1);
T temp = shuffled[i];
shuffled[i] = shuffled[j];
shuffled[j] = temp;
}
// Copy the first N items into the result list
List<T> result = new List<T>();
for (int i = 0; i < count; i++) {
result.Add(shuffled[i]);
}
return result;
}
}
}
/*
run:
Original List:
Apple
Banana
Orange
Mango
Grape
Pineapple
Peach
Cherry
Kiwi
Strawberry
Randomly Selected 3 Items:
Apple
Orange
Kiwi
*/
