List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 };

IEnumerable<int> distinctAges = ages.AsQueryable().Distinct();

Console.WriteLine("Distinct ages:");

foreach (int age in distinctAges)
    Console.WriteLine(age);

//引入命名空间
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {
        int[] factorsOf300 = { 2, 2, 3, 5, 5 };

        int uniqueFactors = factorsOf300.Distinct().Count();

        Console.WriteLine("There are {0} unique factors of 300.", uniqueFactors);
    }
}