hashset

问题 What Initial Capacity should I use for a HashSet into which I know that I am going to insert 1000 integers to prevent the need for any internal rebuilds ? At first I though that I should use 1000 but reading the description of the constructor that taks the initialCapacity parameter it says Constructs a new, empty set; the backing HashMap instance has the specified initial capacity and default load factor (0.75). . So If I set capacity to 1000 the hashMap will resize when reaching 750 elements

问题 Edit: I will add some benchmark results. To about a 1000 - 5000 items in the list, IList and RemoveAt beats ISet and Remove , but that's not something to worry about since the differences are marginal. The real fun begins when collection size extends to 10000 and more. I'm posting only those data I was answering a question here last night and faced a bizarre situation. First a set of simple methods: static Random rnd = new Random(); public static int GetRandomIndex<T>(this ICollection<T>

问题 Currently I have a solution where I keep track of objects I am interested in by getting their hashcode via Object.GetHashCode and then storing them in a HashSet<int> . However, I have also been learning about bitmasks and bitwise operations and I am quite intrigued by them. Here is a great question that I found close to what I am looking to do. However, I cannot seem to make this work efficiently for hash codes. There is also this question, but it seems to deal with 5-bit numbers, when hash

问题 This is my code for now: File file1 = new File("file1.csv"); File file2 = new File("file2.csv"); HashSet<String> f1 = new HashSet<>(FileUtils.readLines(file1)); HashSet<String> f2 = new HashSet<>(FileUtils.readLines(file2)); f2.removeAll(f1); With removeAll() I remove all duplicates wich are in file2 from file1, but now I want to avoid to create a new csv file to optimize the process. Just want to delete from file2 the duplicate rows. Is this possible or I have to create a new file? 回答1: now

问题 This question already has answers here : How to find 3 numbers in increasing order and increasing indices in an array in linear time (13 answers) is it possible to find all the triplets in the given array for the O (n) time? (1 answer) Closed 3 years ago . A decreasing triple is defined as a set of 3 values {a, b, c} that decrease in magnitude from left to right such that a > b > c. How could one find the number of these triples in an array of integers where the indices of the triple {i, j, k

问题 How do i remove the key value pair in the code below comparing with elements in HashMap? Map<BigDecimal, TransactionLogDTO> transactionLogMap = new HashMap<BigDecimal, TransactionLogDTO>(); for (BigDecimal regionID : regionIdList) {// Generation new logDTO // objects for each in scope // region transactionLogMap.put(regionID, new TransactionLogDTO()); } Set<BigDecimal> inScopeActiveRegionIdSet = new HashSet<BigDecimal>(); for (PersonDTO personDTO4 : activePersons) { inScopeActiveRegionIdSet

问题 I'm running some benchmarks. One of my tests depends on order, so I'm using a TreeSet for that. My second test doesn't, so I'm using a HashSet for it. I know that insertion is slower for the TreeSet. But what about iterating through all elements? 回答1: From a similar post (Hashset vs Treeset): HashSet is much faster than TreeSet (constant-time versus log-time for most operations like add, remove and contains) but offers no ordering guarantees like TreeSet. HashSet: class offers constant time

问题 Good morning guys I have a hashset which has different objects Object has attributes GroupName MachineName EmailAddress Now from the HashSet I have to find the Object which has same MachineName and EmailAddress but different Group and add into an arraylist. thanks 回答1: A big assumption is that you are using Java: Set<YourObject> yourHashSet = // List<YourObject> result = new ArrayList<YourObject>(); for( YourObject o: yourHashSet ){ if( o.getMachineName().equals("machine1") && o

问题 Why does containsAll method on a HashSet does not remain consistent if remove is called on the Set whereas a containsValue method on a HashMap remains consistent after a value is removed After a value is removed from a HashSet containsAll returns false even if all values were present where as in case of HashMap the containsValue method returns correct value public static void main(String[] args) { HashSet<String> lookup=new HashSet<String>(); HashMap<Integer,String> findup=new HashMap<Integer

问题 I am using CopyOnWriteArraySet in the following class because I simply like its thread-safe iterator. public class MyClass{ Set _children = new CopyOnWriteArraySet(); public void setChildren(Set children){ _children = children; } public Set getChildren(){ return _children; } } However, I also use Hibernate for persistency which replaces my CopyOnWriteArraySet with its own PersistentSet (which uses HashSet internally). Unfortunately, HashSet is not thread-safe, so I want my CopyOnWriteArraySet