如何使用LINQ计算列表中的重复项

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 1, 2, 5, 6, 6, 7 };

        var duplicates = numbers.GroupBy(x => x)
                                 .Where(g => g.Count() > 1)
                                 .Select(g => g.Key);

        foreach (var duplicate in duplicates)
        {
            Console.WriteLine("重复项：" + duplicate);
        }
    }
}