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问题 Let's say I have the following: struct MetadataThingy { void *actual_thingy; int some_metadata; int more_metadata; bool operator<(MetadataThingy const& other) const { return actual_thingy < other.actual_thingy; } }; where actual_thingy points to some data of importance and I want the container ordered by the value of actual_thingy rather than the value of the element pointed at, but I need to store some other data about it, so I created the wrapper class MetadataThingy with a comparator that

问题 I have two maps as below : Map<String, Record> sourceRecords; Map<String, Record> targetRecords; I want to get the keys differ from each of the maps.i.e. It shows mapping keys available in sourceRecords but not in targetRecords. It shows mapping keys available in targetRecords but not in sourceRecords. I did it as below : Set<String> sourceKeysList = new HashSet<String>(sourceRecords.keySet()); Set<String> targetKeysList = new HashSet<String>(targetRecords.keySet()); SetView<String>

问题 I have looked this up on the net but I am asking this to make sure I haven't missed out on something. Is there a built-in function to convert HashSets to Lists in C#? I need to avoid duplicity of elements but I need to return a List. 回答1: Here's how I would do it: using System.Linq; HashSet<int> hset = new HashSet<int>(); hset.Add(10); List<int> hList= hset.ToList(); HashSet is, by definition, containing no duplicates. So there is no need for Distinct . 回答2: Two equivalent options: HashSet

问题 I want to create a custom set that will automatically convert objects into a different form for storage in the set (see Using a Python Dictionary as a key non-nested) for background. If I override add , remove , __contains__ , __str__ , update , __iter__ , will that be sufficient to make the other operations behave properly, or do I need to override anything else? 回答1: Working from collections 's abstract classes, as @kaizer.se suggests, is the appropriate solution in 2.6 (not sure why you

问题 How do multisets work? If a set can't have a value mapped to a key, does it only hold keys? Also, how do associative containers work? I mean vector and deque in the memory is located sequentially it means that deleting/removing (except beginning [deque] and end [vector, deque]) are slow if they are large. And list is a set of pointers which are not sequentially located in the memory which causes longer search but faster delete/remove. How are sets, maps, multisets and multimaps stored and how

问题 I am learning C#, and am learning about making fields private to the class, and using Getters and Setters to expose Methods instead of field values. Are the get; set; in Method 1 and Method 2 equivalent? e.g. is one a shorthand of the other? class Student { // Instance fields private string name; private int mark; // Method 1 public string Name { get; set; } // Method 2 public int Mark { get { return mark; } set { mark = value; } } } Finally, would Method 2 be used when you want to for

问题 The standard way of intersecting two sets in C++ is to do the following: std::set<int> set_1; // With some elements std::set<int> set_2; // With some other elements std::set<int> the_intersection; // Destination of intersect std::set_intersection(set_1.begin(), set_1.end(), set_2.begin(), set_2.end(), std::inserter(the_intersection, the_intersection.end())); How would I go about doing an in-place set intersection? That is, I want set_1 to have the results of the call to set_intersection.

问题 I have this before the process: protected void onPostExecute(SortedSet<RatedMessage> result) { List<Object> list=Arrays.asList(result.toArray()); lancon.putExtra("results", list.toArray()); // as serializable } then in the other part I have Object o=this.getIntent().getSerializableExtra("results"); //at this point the o holds the correct value (checked by debugger) RatedMessage[] rm = (RatedMessage[]) o;// this line hangs out w ClassCastException resultSet = new TreeSet<RatedMessage>(new Comp

问题 public class SomeClass { private HashSet<SomeObject> contents = new HashSet<SomeObject>(); private Set<SomeObject> contents2 = new HashSet<SomeObject>(); } What's the difference? In the end they are both a HashSet isn't it? The second one looks just wrong to me, but I have seen it frequently used, accepted and working. 回答1: Set is an interface, and HashSet is a class that implements the Set interface. Declaring the variable as type HashSet means that no other implementation of Set may be used

问题 Inspired when answering the question of How do I know if a value of an element inside an array was changed?, The answer was using a Property Observer for checking if an array has been modified. However, How can I determine what is/are the updated element(s) in a collection type in a property observer? For example: class MyClass { var strings: [String] = ["hello", "world", "!"] { didSet(modifiedStrings) { print("strings array has been modified!!:") print(modifiedStrings) } } } let myClass =