using System;
using System.Collections.Generic;
using System.Linq;
public static class Program
{
/// <summary>
/// Finds the element with the minimum number of occurrences in a sequence.
/// </summary>
/// <typeparam name="T">The type of elements in the collection.</typeparam>
/// <param name="source">The source collection to evaluate.</param>
/// <returns>
/// An optional tuple containing the element and its occurrence count,
/// or null if the collection is null or contains no elements.
/// </returns>
public static Tuple<T, int> MinOccurrence<T>(this IEnumerable<T> source)
{
if (source == null) {
return null;
}
// 1. Group items and order by frequency count ascending (Mono/LINQ compatible)
var minGroup = source
.Where(item => item != null)
.GroupBy(item => item)
.OrderBy(group => group.Count())
.FirstOrDefault();
if (minGroup == null) {
return null;
}
return Tuple.Create(minGroup.Key, minGroup.Count());
}
public static void Main(string[] args)
{
int[] arr = new int[] {1, 3, 1, 1, 4, 4, 5, 5, 4, 2, 2, 2, 3, 3, 3};
var result = arr.MinOccurrence();
if (result != null) {
Console.WriteLine(result.Item1); // Output: 5
}
else {
Console.WriteLine("The array was empty or null.");
}
}
}
/*
run:
5
*/
