comparator

问题 I am using struct minHeap to generate a min heap using priority_queue .And function comp to print numbers in reverse order using sort function given in STL . Now my doubt is that I can not use struct minHeap in function sort and can not use function comp in priorityQueue . I feel that function of both struct minHeap and comp is similar. Please explain me when to use structs for comaprator and when to use normal functions to behave as comparators in STL ? #include<iostream> #include <queue>

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: why does my compare method throw exception — Comparison method violates its general contract! I've this code: class TimeComparatorTipo0 implements Comparator { @Override public int compare(Object a, Object b) { String Time1 = ((DataImportedTipo0) a).ora; Long VolTot1 = Long.parseLong(((DataImportedTipo0) a).volume_totale); String Time2 = ((DataImportedTipo0) b).ora; Long VolTot2 = Long.parseLong((

问题 In a method I receive a generic object E extends Comparable<E> as an argument. Now i want to create two priority queues.One which uses the comparator used by E and other queue which uses the opposite of comparator used by E(i.e. if E uses '<' then second queue must use '>='). Please hep me how to create two such queues. queue2=new PriorityQueue<E>(0,Collections.reverseOrder(e)); I am getting the error that reverseOrder is not applicable. please help 回答1: Look at Collections.reverseOrder. 回答2:

问题 I have a class that I would like to use in a scala.collection.mutable.PriorityQueue, but I don't want to make it Ordered[A] just for this one purpose. I don't consider the ordering I want to use with respect to the PriorityQueue as the natural ordering of the class. class MyObject (sequence: Int, values: List[String]) ... So, in my PriorityQueue, I would like the values to be ordered by 'sequence'. However, just because two objects have the same sequence doesn't make them naturally equal

问题 This question already has answers here : The built-in iterator for java's PriorityQueue does not traverse the data structure in any particular order. Why? (5 answers) Closed 3 years ago . I've written a custom comparator to compare my node classes, but the java priority queue is not returning my items in the correct order. Here is my comparator: public int compare(Node n1, Node n2){ if (n1.getF() > n2.getF()){ return +1; } else if (n1.getF() < n2.getF()){ return -1; } else { // equal return 0

问题 Let's have a class Person . Person has a name and height. Equals and hashCode() takes into account only name. Person is comparable (or we implement comparator for it, does not matter which one). Persons are compared by height. It seems reasonable to expect a situation where two different persons can have same height, but eg. TreeSet behaves like comapareTo()==0 means equals, not merely same size. To avoid this, comparison can secondarily look at something else if size is the same, but then it

问题 Let's have a class Person . Person has a name and height. Equals and hashCode() takes into account only name. Person is comparable (or we implement comparator for it, does not matter which one). Persons are compared by height. It seems reasonable to expect a situation where two different persons can have same height, but eg. TreeSet behaves like comapareTo()==0 means equals, not merely same size. To avoid this, comparison can secondarily look at something else if size is the same, but then it

问题 Suppose I need TreeSet with elements sorted with some domain logic. By this logic it doesn't matter order of some elements that doesn't equal so compare method can return 0, but in this case I couldn't put them in TreeSet . So, question: what disadvantages I'll have from code like this: class Foo implements Comparable<Foo>{} new TreeSet<Foo>(new Comparator<Foo>(){ @Override public int compare(Foo o1, Foo o2) { int res = o1.compareTo(o2); if(res == 0 || !o1.equals(o2)){ return o1.hashCode() -

问题 Below is a block of code that results in exception as indicated, Code : Collections.sort( arrayList, new Comparator() { public int compare( Object o1, Object o2 ) { TypeAdapterSort tas1 = ( TypeAdapterSort ) o1; TypeAdapterSort tas2 = ( TypeAdapterSort ) o2; if ( tas1.order < tas2.order ) return -1; else return 1; } } ); Exception : java.lang.IllegalArgumentException: Comparison method violates its general contract! at java.util.TimSort.mergeLo(TimSort.java:747) at java.util.TimSort.mergeAt

问题 Im trying to learn comparator in java and I have found this great example online, my question is how would this code be changed so that the pet names are ordered by age and in descending order so that the oldest is first and youngest is last? class Dog implements Comparator<Dog>, Comparable<Dog>{ private String name; private int age; Dog(){ } Dog(String n, int a){ name = n; age = a; } public String getDogName(){ return name; } public int getDogAge(){ return age; } // Overriding the compareTo