如何使用ExceptWith类型的HashSet >在C＃中？

Question

HashSet<ReadOnlyCollection<int>> test1 = new HashSet<ReadOnlyCollection<int>> ();
for (int i = 0; i < 10; i++) {
    List<int> temp = new List<int> ();
    for (int j = 1; j < 2; j++) {
        temp.Add (i);
        temp.Add (j);
    }
    test1.Add (temp.AsReadOnly ());
}

这里test1是{[0,1]，[1,1]，[2,1]，[3,1]，[4,1]，[5,1]，[6,1]，[7 ，1]，[8,1]，[9,1]}

HashSet<ReadOnlyCollection<int>> test2 = new HashSet<ReadOnlyCollection<int>> ();
for (int i = 5; i < 10; i++) {
    List<int> temp = new List<int> ();
    for (int j = 1; j < 2; j++) {
        temp.Add (i);
        temp.Add (j);
    }
    test2.Add (temp.AsReadOnly ());
}

这里test2是{[5,1]，[6,1]，[7,1]，[8,1]，[9,1]}

test1.ExceptWith(test2);

完成此操作后，我希望test1为{[0,1]，[1,1]，[2,1]，[3,1]，[4,1]}，但它给了我原始的test1 。如何解决这个问题？还是有其他方法可以做同样的事情？谢谢！

Answer 1

这里您具有ExceptWith的实现：

https://github.com/microsoft/referencesource/blob/3b1eaf5203992df69de44c783a3eda37d3d4cd10/System.Core/System/Collections/Generic/HashSet.cs#L532

其实际作用是：

 // remove every element in other from this
 foreach (T element in other) {
    Remove(element);
 }

并删除：

https://github.com/microsoft/referencesource/blob/3b1eaf5203992df69de44c783a3eda37d3d4cd10/System.Core/System/Collections/Generic/HashSet.cs#L287

 if (m_slots[i].hashCode == hashCode && m_comparer.Equals(m_slots[i].value, item)) {

因此，如果哈希码不同，则跳过它一个小测试：

    List<int> temp = new List<int> ();
     temp.Add(1);
     temp.Add(2);

    HashSet<ReadOnlyCollection<int>> test1 = new HashSet<ReadOnlyCollection<int>> ();
    HashSet<ReadOnlyCollection<int>> test2 = new HashSet<ReadOnlyCollection<int>> ();
    test1.Add (temp.AsReadOnly ());
    test2.Add (temp.AsReadOnly ());

    Console.WriteLine(test1.First().GetHashCode() == test2.First().GetHashCode());