Linq的Except

https://msdn.microsoft.com/en-us/library/bb300779(v=vs.100).aspx

  var list1 = new List<int> {1, 2, 3, 4};
        var list2 = new List<int> {2, 3, 5, 6};
        var list = list1.Except(list2);
        foreach (var item in list)
        {
            Console.WriteLine(item);
        }

        Console.WriteLine("===============");

        list = list2.Except(list1);
        foreach (var item in list)
        {
            Console.WriteLine(item);
        }