set

问题 Java has a LinkedHashSet, which is a set with a predictable iteration order. What is the closest available data structure in C++? Currently I'm duplicating my data by using both a set and a vector. I insert my data into the set. If the data inserted successfully (meaning data was not already present in the set), then I push_back into the vector. When I iterate through the data, I use the vector. 回答1: If you can use it, then a Boost.MultiIndex with sequenced and hashed_unique indexes is the

问题 I have a Java EE application and I use Hibernate. The domain objects, I changed the List / ArrayList to Set / HashSet, because it is better to use Sets. But in my Dao implementation I run into a problem: public Set<Person> getAllPersons() { SessionFactory sessionFactory = HibernateUtil.getSessionFactory(); Session sess = sessionFactory.getCurrentSession(); Transaction tx = sess.beginTransaction(); @SuppressWarnings("unchecked") Set<Item> items = (Set<Item>) sess.createQuery("from Item").list(

问题 According to this page, I can achieve constant time insertion if I use iterator std::set::insert ( iterator position, const value_type& x ); and the position iterator I provide directly "precedes" the proper (in-order) insertion point. Now the case I'm concerned with is if I know that the value I'm inserting goes at the end (since it's the largest), e.g.: set<int> foo = {1, 2, 3}; foo.insert(4); // this is an inefficient insert According to the above criterion I should pass the last element

问题 I have two large files. Their contents looks like this: 134430513 125296589 151963957 125296589 The file contains an unsorted list of ids. Some ids may appear more than one time in a single file. Now I want to find the intersection part of two files. That is the ids appear in both files. I just read the two files into 2 sets, s1 and s2 . And get the intersection by s1.intersection(s2) . But it consumes a lot of memory and seems slow. So is there any better or pythonic way to do this? If the

问题 This question already has answers here : Javascript ES6 computational/time complexity of collections (2 answers) Closed 9 months ago . I have seen in an answer that the Set.has() method is O(1) and Array.indexOf() is O(n). var a = [1, 2, 3, 4, 5]; a.indexOf(5); s = new Set(a); s.has(5); //Is this O(1)? Is Set.has() really O(1) ? 回答1: If one read the specification of has() , there is an algorithm describing it: Algorithm for Set.prototype.has(value) : The following steps are taken: Let S be

问题 Lets say I have the following document: {name: 'myDoc', nestedDoc: {a: 1, b: 2, c: 3}} And I would like to merge with the nestedDoc a new object: {b: 20, c:30, d:40} So the resulting object would be: {name: 'myDoc', nestedDoc: {a: 1, b: 20, c: 30, d: 40}} How can I go about doing this in a single query? I feel like I need multiple $set calls however object property names must be unique. In other words, I wish I could do the following: db.myCollection.update({name: 'myDoc', nestedDoc: {$set:

问题 There are two ways in which I can easily make a key,value attribution in C++ STL: maps and sets of pairs. For instance, I might have map<key_class,value_class> or set<pair<key_class,value_class> > In terms of algorithm complexity and coding style, what are the differences between these usages? 回答1: Set elements cannot be modified while they are in the set. set 's iterator and const_iterator are equivalent. Therefore, with set<pair<key_class,value_class> > , you cannot modify the value_class

问题 I am making a particle emitter. Every "Rendered" object is stored in a HashSet, and when there's lots of particles on the screen, the console spits out concurrent modification exceptions. I usually have a short lifetime on these particles so they get deleted after several seconds, but I am sure this could potentially be a problem in the future. How can I fix this? EDIT: Code: public class UpdatedManager { private static Set<Updated> updates = new HashSet<>(); private UpdatedManager() {}

问题 My question is pretty simple but I'm not sure if it's possible. Assume I have a table and it contains the column below PokemonHappiness smallint Is it possible to set a maximum value for that column? For instance if I set the maximum to 10000 and send a query like this --Assume that PokemonHappiness is equal to 9990 update mytable set PokemonHappiness = PokemonHappiness+50 it should become 10000 instead of 10040 Is this possible? 回答1: A trigger. I tested this. CREATE TRIGGER dbo.Table_2update

问题 Given an array of elements in PHP, I wish to create a new two-dimensional array containing only those elements of the power set that are a specific length. As an example, for the following array: array(4) { 0 => 'A', 1 => 'B', 2 => 'C', 3 => 'D' } If I were to run the function fixed_length_power_set( $arr, 2 ) then I want it to return: array(6) { 0 => array(2) { 0 => 'A', 1 => 'B' } 1 => array(2) { 0 => 'A', 1 => 'C' } 2 => array(2) { 0 => 'A', 1 => 'D' } 3 => array(2) { 0 => 'B', 1 => 'C' }