Hello I would like to define my own class collection, and make it iterable in a foreach statement, just like this :
public class Collection(Type)
{
...
private T head;
private Collection!(T) queue;
}
Collection!(int) temp;
foreach (int t; temp) { ... }
What methods should I define, and how ?
you can specify the front, popfront() and empty functions: (but this will consume your collection unless you use save())
public class Collection(T) { ... private T head; private Collection!(T) queue;
#property T front(){
return head;
}
#property bool empty(){
return queue is null;
}
void popfront(){
head = queue.head;
queue = queue.queue;
}
Collection!T save(){
return new Collection!T(head,queue);
}
}
or use a dedicated struct for iteration (as is done in the std.container module
public class Collection(T) { ... private T head; private Collection!(T) queue;
Range opSlice(){
return Range(head,queue);
}
struct Range{
T h;
Collection!(T) q;
this(T he, Collection!(T) qu){
h=he;
q=qu;
}
#property T front(){
return h;
}
#property bool empty(){
return q is null;
}
void popfront(){
h = q.head;
q= q.queue;
}
Collection!T save(){
return this;
}
}
}
so iteration is done like so
Collection!(int) temp; foreach (int t;temp[]) { ... }
you also can add an opApply for the normal foreach:
public int opApply(int delegate(ref T) dg){
int res=0;
foreach(ref T;this[]){
res = dg(t);
if(res)return res;
}
return res;
}
Take a look at this documentation on ForeachStatements and scroll down a bit.
If I'm reading your example correctly, you could define an opApply for Collection as follows:
public int opApply(int delegate(ref T) dg){
Collection!T p = this;
int res = 0;
while(!res && p !is null){
res = dg(p.head);
p = p.queue;
}
return res;
}
Your Collection class should implement opApply. Your foreach body becomes a delegate to an internal for loop, and you iterate over your internal collection (in your case a queue) using a for loop.
Consider the example given in the docs
class Foo {
uint array[2];
int opApply(int delegate(ref uint) dg)
{ int result = 0;
for (int i = 0; i < array.length; i++)
{
result = dg(array[i]);
if (result)
break;
}
return result;
}
}
Related
I have the below code that is creating the PriortyQueue structure using Dart. But since I cannot use heapify function inside the Constructor or factory constructor I cannot initialize PQ with an existing set of List. Can somebody guide me and show me how I can use heapify while creating PQ instance so I can initialize it with an existing List? Also If you have any other suggestions against doing something like this please also help me as well. thank you
class PriorityQueue<T extends Comparable<T>> {
List<T?> _tree;
PriorityQueue._(List<T?> tree) : _tree = tree;
factory PriorityQueue([List<T>? array]) {
List<T?> newArray = [null, ...array ?? []];
// ignore: todo
//TODO: missing heapify
return PriorityQueue._(newArray);
}
void insert(T node) {
_tree.add(node);
_swim(_tree.length - 1);
}
T getTop() {
_swap(1, _tree.length - 1);
T top = _tree.removeLast() as T;
_sink(1);
return top;
}
List<T> _heapify(List<T> array) {
int sinkNodeIndex = (array.length - 1) ~/ 2;
while (sinkNodeIndex >= 1) {
_sink(sinkNodeIndex);
sinkNodeIndex--;
}
}
void _sink(int nodeIndex) {
int leftChildIndex = nodeIndex * 2;
int rightChildIndex = leftChildIndex + 1;
int minNodeIndex = leftChildIndex;
// index can be unreachable
T? leftChild =
leftChildIndex >= _tree.length ? null : _tree[leftChildIndex];
T? rightChild =
rightChildIndex >= _tree.length ? null : _tree[rightChildIndex];
if (leftChild == null) {
return;
}
if (rightChild != null && leftChild.compareTo(rightChild) > 0) {
minNodeIndex = rightChildIndex;
}
if ((_tree[minNodeIndex] as T).compareTo(_tree[nodeIndex] as T) < 0) {
_swap(nodeIndex, minNodeIndex);
_sink(minNodeIndex);
}
}
void _swim(int nodeIndex) {
if (nodeIndex <= 1) return;
int parentIndex = nodeIndex ~/ 2;
if ((_tree[nodeIndex] as T).compareTo(_tree[parentIndex] as T) < 0) {
_swap(nodeIndex, parentIndex);
_swim(parentIndex);
}
}
void _swap(int i, int j) {
T temp = _tree[i] as T;
_tree[i] = _tree[j];
_tree[j] = temp;
}
#override
String toString() {
return _tree.toString();
}
}
I would make all the helper functions. _heapify, _sink/_swim, even _swap, be static functions which take the list as argument.
Then you can use them from anywhere, including inside the factory constructor.
Alternatively, you can change the constructor to returning:
return PriorityQueue._(newArray).._heapify();
This creates the PriorityQueue object, and then calls the _heapify method on it, before returning the value.
(I'd also make _tree have type List<T> and not insert the extra null at the beginning. It's more efficient to add/subtract 1 from indices than it is to cast to T.)
I ended up doing like Irn's first suggestion. But when I do functions static they lost Type of the class so I needed to specify for each function. Also, making List<T?> instead of List ended up with me fighting against the compiler.
class PriorityQueue<T extends Comparable<T>> {
List<T?> _tree;
PriorityQueue._(List<T?> tree) : _tree = tree;
factory PriorityQueue([List<T>? array]) {
List<T?> newArray = [null, ...array ?? []];
_heapify(newArray);
return PriorityQueue._(newArray);
}
bool get isNotEmpty {
return _tree.isNotEmpty;
}
void insert(T node) {
_tree.add(node);
_swim(_tree, _tree.length - 1);
}
void insertMultiple(List<T> array) {
for (var element in array) {
insert(element);
}
}
T? removeTop() {
if (_tree.length == 1) return null;
_swap(_tree, 1, _tree.length - 1);
T top = _tree.removeLast() as T;
_sink(_tree, 1);
return top;
}
void removeAll() {
_tree = [null];
}
static void _heapify<T extends Comparable<T>>(List<T?> array) {
int sinkNodeIndex = (array.length - 1) ~/ 2;
while (sinkNodeIndex >= 1) {
_sink(array, sinkNodeIndex);
sinkNodeIndex--;
}
}
static void _sink<T extends Comparable<T>>(List<T?> tree, int nodeIndex) {
int leftChildIndex = nodeIndex * 2;
int rightChildIndex = leftChildIndex + 1;
int minNodeIndex = leftChildIndex;
T? leftChild = leftChildIndex >= tree.length ? null : tree[leftChildIndex];
T? rightChild =
rightChildIndex >= tree.length ? null : tree[rightChildIndex];
if (leftChild == null) {
return;
}
if (rightChild != null && leftChild.compareTo(rightChild) > 0) {
minNodeIndex = rightChildIndex;
}
if ((tree[minNodeIndex] as T).compareTo(tree[nodeIndex] as T) < 0) {
_swap(tree, nodeIndex, minNodeIndex);
_sink(tree, minNodeIndex);
}
}
static void _swim<T extends Comparable<T>>(List<T?> tree, int nodeIndex) {
if (nodeIndex <= 1) return;
int parentIndex = nodeIndex ~/ 2;
if ((tree[nodeIndex] as T).compareTo(tree[parentIndex] as T) < 0) {
_swap(tree, nodeIndex, parentIndex);
_swim(tree, parentIndex);
}
}
static void _swap<T extends Comparable<T>>(List<T?> tree, int i, int j) {
T temp = tree[i] as T;
tree[i] = tree[j];
tree[j] = temp;
}
#override
String toString() {
return _tree.toString();
}
}
Below I have the int indexOf(T element) method for a double linked list. I need help with the code to make sure it functions properly. The method should return the first occurence of the element in the list or -1 if element is not in the list. Below is the node class it uses. The IUDoubleLinkedList.java class implements IndexedUnsortedList.java which is where the indexOf method comes from. I tried using my indexOf method from my single linked list class but it's not the same so I hope to understand why it would be different and what code is used that is different between the the single and double linked list.
public class IUDoubleLinkedList<T> implements IndexedUnsortedList<T> {
private Node<T> head, tail;
private int size;
private int modCount;
public IUDoubleLinkedList() {
head = tail = null;
size = 0;
modCount = 0;
This is the indexOf(T element) method
#Override
public int indexOf(T element) {
// TODO Auto-generated method stub
return 0;
}
Below is the Node.java class it uses
public class Node<T> {
private Node<T> nextNode;
private T element;
private Node<T> prevNode;
/**
* Creates an empty node.
*/
public Node() {
nextNode = null;
element = null;
}
/**
* Creates a node storing the specified element.
*
* #param elem
* the element to be stored within the new node
*/
public Node(T element) {
nextNode = null;
this.element = element;
setPrevNode(null);
}
/**
* Returns the node that follows this one.
*
* #return the node that follows the current one
*/
public Node<T> getNextNode() {
return nextNode;
}
/**
* Sets the node that follows this one.
*
* #param node
* the node to be set to follow the current one
*/
public void setNextNode(Node<T> nextNode) {
this.nextNode = nextNode;
}
/**
* Returns the element stored in this node.
*
* #return the element stored in this node
*/
public T getElement() {
return element;
}
/**
* Sets the element stored in this node.
*
* #param elem
* the element to be stored in this node
*/
public void setElement(T element) {
this.element = element;
}
#Override
public String toString() {
return "Element: " + element.toString() + " Has next: " + (nextNode != null);
}
public Node<T> getPrevNode() {
return prevNode;
}
public void setPrevNode(Node<T> prevNode) {
this.prevNode = prevNode;
}
}
Check the following code, hope I helped you!
Insert item at head as well as tail end
public void insertItem(T elem) {
/* if head and tail both are null*/
if(head == null || tail == null) {
head = new Node<T>(elem);
tail = new Node<T>(elem);
}else {
Node<T> tempItem = new Node<T>();
tempItem.setElement(elem);
/* insert at head end /*
tempItem.setNextNode(head);
head.setPrevNode(tempItem);
head = tempItem;
Node<T> tempItem1 = new Node<T>();
tempItem1.setElement(elem);
/* append at tail end */
tail.setNextNode(tempItem1);
tempItem1.setPrevNode(tail);
tail = tempItem1;
}
size += 1;
}
Print item from head end
public void printItemsFromHead() {
while(head != null) {
System.out.print(head.getElement()+" --> ");
head = head.getNextNode();
}
}
Print item from tail end
public void printItemsFromTail() {
Node<T> temp = null;
while(tail != null) {
temp = tail;
System.out.print(tail.getElement()+" --> ");
tail = tail.getPrevNode();
}
/*System.out.println();
while(temp != null) {
System.out.print(temp.getElement()+" --> ");
temp = temp.getNextNode();
}*/
}
Implemention of indexOf function
#Override
public int indexOf(T element) {
int result = -1;
int headIndex = 0;
int tailIndex = size;
while(head != null && tail != null) {
if(head.getElement().equals(element)) {
result = headIndex;
break;
}
/*
if(tail.getElement().equals(element)) {
result = tailIndex;
break;
} */
head = head.getNextNode();
tail = tail.getPrevNode();
headIndex += 1;
tailIndex -= 1;
}
return result;
}
Driver class
public class Driver {
#SuppressWarnings({ "rawtypes", "unchecked" })
public static <T> void main(String[] args) {
UDoubleLinkedList uDoubleLinkedList = new UDoubleLinkedList();
uDoubleLinkedList.insertItem(1);
uDoubleLinkedList.insertItem(2);
uDoubleLinkedList.insertItem(3);
uDoubleLinkedList.insertItem(4);
uDoubleLinkedList.insertItem(5);
System.out.println(uDoubleLinkedList.indexOf(1));
}
}
The following code illustrates a logic I need in a Spring Reactive project:
Inputs:
var period = 3;
int [] inArr = {2, 4, 6, 7, 9, 11, 13, 16, 17, 18, 20, 22 };
Calculation:
var upbond = inArr[0] + period;
var count =0;
List<Integer> result = new ArrayList();
for(int a: inArr){
if(a <= upbond){
count++;
}else{
result.add(count);
count = 1;
upbond += period;
}
}
result.add(count);
System.out.println(Arrays.toString(result.toArray()));
The data source of the sorted integers is the Flux from DB where it shall continually fetch data once a new suitable data is written into the DB. And the result shall be a stream that is sending out to another node through RSocket (by the request-stream communication mode).
After some online searching on Reactor, including some tutorials, I still can't figure out how to write the logic in the Flux fashion. The difficulty I have is that those calculations on data defined outside of the loop.
How shall I approach it in the Reactor?
The scan() variant that lets you use a separately typed accumulator is your friend here.
I'd approach this with a separate State class:
public class State {
private int count;
private Optional<Integer> upbond;
private Optional<Integer> result;
public State() {
this.count = 0;
this.upbond = Optional.empty();
this.result = Optional.empty();
}
public State(int count, int upbond) {
this.count = count;
this.upbond = Optional.of(upbond);
this.result = Optional.empty();
}
public State(int count, int upbond, int result) {
this.count = count;
this.upbond = Optional.of(upbond);
this.result = Optional.of(result);
}
public int getCount() {
return count;
}
public Optional<Integer> getUpbond() {
return upbond;
}
public Optional<Integer> getResult() {
return result;
}
}
...and then use scan() to build up the state element by element:
sourceFlux
.concatWithValues(0)
.scan(new State(), (state, a) ->
a <= state.getUpbond().orElse(a + period) ?
new State(state.getCount() + 1, state.getUpbond().orElse(a + period)) :
new State(1, state.getUpbond().orElse(a + period) + period, state.getCount())
)
.windowUntil(s -> s.getResult().isPresent())
.flatMap(f -> f.reduce((s1, s2) -> s1.getResult().isPresent()?s1:s2).map(s -> s.getResult().orElse(s.getCount() - 1)))
Aside: The concatWithValues() / windowUntil() / flatMap() bits are there to handle the last element - there's probably a cleaner way of achieving that, if I think of it I'll edit the answer.
I think scan is definitely the right tool here, combined with a stateful class, although my approach would be slightly different than Michaels.
Accumulator:
class UpbondAccumulator{
final Integer period;
Integer upbond;
Integer count;
Boolean first;
Queue<Integer> results;
UpbondAccumulator(Integer period){
this.period = period;
this.count = 0;
this.upbond = 0;
this.results = new ConcurrentLinkedQueue<>();
this.first = true;
}
//Logic is inside accumulator, since accumulator is the only the only thing
//that needs it. Allows reuse of accumulator w/o code repetition
public UpbondAccumulator process(Integer in){
//If impossible value
//Add current count to queue and return
//You will have to determine what is impossible
//Since we concat this value on the end of flux
//It will signify the end of processing
//And emit the last count
if(in<0){
results.add(count);
return this;
}
//If first value
//Do stuff outside loop
if(this.first) {
upbond = in + period;
first=false;
}
//Same as your loop
if(in <= upbond)
count++;
else {
results.add(count);
count = 1;
upbond += period;
}
//Return accumulator
//This could be put elsewhere since it isn't
//Immediately obvious that `process` should return
//the object but is simpler for example
return this;
}
public Mono<Integer> getResult() {
//Return mono empty if queue is empty
//Otherwise return queued result
return Mono.justOrEmpty(results.poll());
}
}
Usage:
dbFlux
//Concat with impossible value
.concatWithValues(-1)
//Create accumulator, process value and return
.scan(new UpbondAccumulator(period), UpbondAccumulator::process)
//Get results, note if there are no results, this will be empty
//meaning it isn't passed on in chain
.flatMap(UpbondAccumulator::getResult)
Following comment from Michael here is an immutable approach
Accumulator:
public class UpbondAccumulator{
public static UpbondState process(int period,Integer in,UpbondState previous){
Integer upbond = previous.getUpbond().orElse(in + period);
int count = previous.getCount();
if(in<0) return new UpbondState(upbond, count, count);
if(in <= upbond) return new UpbondState(upbond,count + 1 , null);
return new UpbondState(upbond + period, 1, count);
}
}
State object:
public class UpbondState {
private final Integer upbond;
private final int count;
private final Integer result;
public UpbondState() {
this.count = 0;
this.upbond = null;
this.result = null;
}
public UpbondState(Integer upbond, int count,Integer result) {
this.upbond = upbond;
this.count = count;
this.result = result;
}
public int getCount() { return count; }
public Optional<Integer> getUpbond() { return Optional.ofNullable(upbond); }
public Integer getResult() { return result; }
public boolean hasResult() { return result!=null; }
}
Usage:
dbFlux
.concatWithValues(-1)
.scan(new UpbondState(),
(prev, in) -> UpbondAccumulator.process(period,in,prev))
//Could be switched for Optional, but would mean one more map
//+ I personally think makes logic less clear in this scenario
.filter(UpbondState::hasResult)
.map(UpbondState::getResult)
//I have a single linked list that looks like this
node head = new Node ();
head.info = 3;
head.next = new Node ();
head.next.info = 6 ();
head.next.next = new Node ();
head.next.next.info = 9;
head.next.next.next = null;
//How would I write a double linked list?
class Double Node
{
info;
doubleNode prev;
doubleNode next;
}
Here is the part for creating a double linked list and adding nodes to it.
You can update it by adding remove and insert functions as you want.
class Node{
Node prev;
Node next;
int value;
public Node(int value) {
this.value = value;
}
}
class DoubleLinkedList{
Node head;
Node tail;
public DoubleLinkedList(Node head) {
this.head = head;
this.tail = head;
head.next = null;
head.prev = null;
}
public void addNode(Node node){
tail.next = node;
node.prev = tail;
tail = node;
}
}
public class Main {
public static void main(String args[]){
Node head= new Node(3);
DoubleLinkedList list = new DoubleLinkedList(head);
list.addNode(new Node(5));
list.addNode(new Node(6));
list.addNode(new Node(7));
list.addNode(new Node(8));
}
}
This would be the idea:
node head = new Node();
head.info = 3;
node prev, actual, next;
prev = head;
actual.prev = prev;
actual.info = 6;
actual = actual.next = new Node();
actual.prev = prev;
actual = actual.next = new Node();
actual.info = 9;
...
Assuming that you will have the behavior in your example, you can automate it with a function, in c# would be something like:
function GetDoubleLinkedList(Node head, int from, int end, int jumps)
{
head.info = from;
node prev = head, actual, next;
for(var i = from+jumps; i <= end; i+=jumps)
{
actual.prev = prev;
actual.info = i;
actual = actual.next = new Node();
}
actual.info = end;
return head;
}
//...
//then you can do
node head = new Node();
head = GetDoubleLinkedList(head, 3, 9, 3);
//...
Double linked list are like single linked list with the exception that they have two pointer in the declaration of structure
a previous pointer and a next pointer
For sample implementation see this link
Here is an implementation of a DoubleLinkedList in Java (along with some examples that might help you understand how it's working):
public class Node {
public int value;
public Node prev;
public Node next;
public Node(int value) {
this.value = value;
this.prev = null;
}
public Node(int value, Node prev) {
this.value = value;
this.prev = prev;
}
public Node add(int value) {
if(this.next == null) {
this.next = new Node(value, this);
} else {
this.next.add(value);
}
return this;
}
public Node last() {
if(this.next == null) {
return this;
} else {
return this.next.last();
}
}
public String toString() {
String out = value+" ";
if(this.next != null) {
out += this.next.toString();
}
return out;
}
public static void main(String...arg) {
Node list = (new Node(3)).add(6).add(5).add(9);
System.out.println(list.toString());
//Output:3 6 5 9
System.out.println(list.last().toString());
//Output:9
System.out.println(list.last().prev.prev.toString());
//Output:6 5 9
}
}
You can use following DoubleLinkedList class.
public class DoubleLinkedList<T>
{
Node<T> start;
Node<T> end;
public void AddFirst(T dataToAdd)
{
Node<T> tmp = new Node<T>(dataToAdd);
if (start == null)
{
start = tmp;
end = start;
return;
}
start.previous = tmp;
tmp.next = start;
start = tmp;
if (start.next == null)
{
end = start;
}
}
public void AddLast(T dataToAdd)
{
if (start == null)
{
AddFirst(dataToAdd);
return;
}
Node<T> tmp = new Node<T>(dataToAdd);
end.next = tmp;
tmp.previous = end;
end = tmp;
}
public T RemoveFirst()
{
if (start == null) return default(T);
T saveVal = start.data;
start = start.next;
start.previous = null;
if (start == null) end = null;
return saveVal;
}
public T RemoveLast()
{
if (start == null) return default(T);
T saveVal = end.data;
end = end.previous;
end.next = null;
if (start == null) end = null;
return saveVal;
}
public void PrintAll()
{
Node<T> tmp = start;
while (tmp != null)
{
Console.WriteLine(tmp.data.ToString());
tmp = tmp.next;
}
}
}
And Use the following Node class
class Node<T>
{
public T data;
public Node<T> next;
public Node<T> previous;
public Node(T newData)
{
data = newData;
next = null;
previous = null;
}
}
I need to sort an array of String like the following, in ascending order.
String str[] = {"ASE", "LSM", "BSE", "LKCSE", "DFM"};
How to do that? I need help.
This answer is based on Signare and HeartBeat's suggestion. Explore this link for details. Also this link, Sorting using java.util.Array might be helpful.
// Initialization of String array
String strs[] = {"One", "Two", "Threee", "Four", "Five", "Six", "Seven"};
// implementation of Comparator
Comparator strComparator = new Comparator() {
public int compare(Object o1, Object o2) {
return o1.toString().compareTo(o2.toString());
}
};
// Sort
Arrays.sort(strs, strComparator);
Try this -
import java.util.*;
import java.io.*;
public class TestSort1 {
String [] words = { "Réal", "Real", "Raoul", "Rico" };
public static void main(String args[]) throws Exception {
try {
Writer w = getWriter();
w.write("Before :\n");
for (String s : words) {
w.write(s + " ");
}
java.util.Arrays.sort(words);
w.write("\nAfter :\n");
for (String s : words) {
w.write(s + " ");
}
w.flush();
w.close();
}
catch(Exception e){
e.printStackTrace();
}
}
// useful to output accentued characters to the console
public static Writer getWriter() throws UnsupportedEncodingException {
if (System.console() == null) {
Writer w =
new BufferedWriter
(new OutputStreamWriter(System.out, "Cp850"));
return w;
}
else {
return System.console().writer();
}
}
}
Here is my solution:-
String str[]={"ASE","LSM","BSE","LKCSE","DFM"};
for(int j = 0; j < str.length; j++){
for(int i = j + 1; i < str.length; i++) {
if(str[i].compareTo(str[j]) < 0) {
String t = str[j];
str[j] = str[i];
str[i] = t;
}
}
}