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what is queue

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Magnificent Moose answered on May 24, 2022 Popularity 9/10 Helpfulness 1/10

answer what is queue

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A queue is a linear list of elements in which deletion can take place only at
one end, called the front, and insertion can take place only at the other end,
called the rare.
// Example: FIFO (First In First Out).
// In other words, the order in which elements enter a queue, is the order in
// which they leave.

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Contributed on Nov 26 2023

Magnificent Moose

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Standard queue

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items are pushed to queue in order, but applications polling or receiving records might get them not in the exact order ( Best-Effort Ordering) and occasionally a copy of the message could be delivered ( At-Least-Once delivery )

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Contributed on Feb 21 2023

Pragya Keshap

0 Answers Avg Quality 2/10

queue

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#include <iostream>
#include <iomanip>

using namespace std;

/*
    Complete Implementation of Queue using Doubly Linked List
*/

struct Node {
    int data;
    Node *next;
    Node *prev;
};

class Queue {
    private:
        Node *front;
        Node *rear;
        int Size;

    public:
        Queue() {
            this->Size = 0;
            this->front = nullptr;
            this->rear = nullptr;
        }

        ~Queue() {
            if (this->isEmpty()) {
                cout << endl << "Nothing to delete!" << endl;
            } else {
                cout << "\n[Desctructor call]" << endl;

                while (this->rear != nullptr) {
                    Node *current = this->rear;

                    this->rear = this->rear->next;
                    cout << " delete: [" << current->data << " | " << current->next << "]" << endl;

                    delete current;
                }
            }
        }

        int size() const {
            return this->Size;
        }

        bool isEmpty() const {
            return (this->front == nullptr);
        }

        int peek() const {
            return (isEmpty()) ? 0 : this->front->data;
        }

        Queue &enqueue(const int &value) {
            Node *node = new Node();

            node->data = value;
            node->next = nullptr;
            node->prev = nullptr;

            if (this->rear == nullptr) {
                this->rear = this->front = node;
            } else {
                node->next = this->rear;
                this->rear->prev = node;
                this->rear = node;
            }

            this->Size++;

            return *this;
        }

        Queue &dequeue() {
            if (this->isEmpty()) {
                cout << "Queue is empty" << endl;
            } else {
                if (this->rear == this->front) {
                    delete this->front;
                    this->front = this->rear = nullptr;
                } else {
                    Node *temp = this->front;
                    this->front = this->front->prev;
                    this->front->next = nullptr;

                    delete temp;
                }
            
                this->Size--;
            }

            return *this;
        }

        void display() const {
            if (this->rear == nullptr) {
                cout << "Rear:  [" << NULL << " | " << this->rear << "] " << endl;
                cout << "Front: [" << NULL << " | " << this->front  << "] " << endl;
            } else {
                Node *current = this->rear;

                while (current != nullptr) {
                    if (current == this->rear) {
                        cout << "Rear: [" << current->data << " | " << current->next << ((current->next == nullptr) ? "] :Front\n" : "] -> ");
                    } else if (current->next == nullptr) {
                        cout << "[" << this->front->data << " | " << this->front->next  << "] :Front" << endl;
                    } else {
                        cout << "[" << current->data << " | " << current << "] -> ";
                    }
                    
                    current = current->next;
                }
            }
        }
};



int main() {
  
    /*      Example usage:  */  
    Queue queue = Queue();

    cout << endl;

    queue.enqueue(1).enqueue(2).enqueue(3);
    queue.display();
    
    queue.dequeue();
    queue.display();

    queue.dequeue().dequeue();
    queue.display();

    queue.enqueue(10);
    queue.enqueue(20);
    queue.enqueue(30);

    cout << std::boolalpha;
    cout << endl;
    cout << "Size:     " << queue.size() << endl; 
    cout << "Front:    " << queue.peek() << endl;
    queue.dequeue() ;
    cout << "Is Empty: " << queue.isEmpty() << endl;
    cout << "Front:    " << queue.peek() << endl;
    queue.dequeue();
    cout << "Is Empty: " << queue.isEmpty() << endl;
    cout << "Front:    " << queue.peek() << endl;
    queue.dequeue(); 
    cout << "Is Empty: " << queue.isEmpty() << endl << endl;

    queue.enqueue(4);
    queue.enqueue(3);
    queue.enqueue(2);
    queue.enqueue(1);
    queue.display();

    /*
        Output:

        Rear: [3 | 0x7fa3a0f05cb0] -> [2 | 0x7fa3a0f05cb0] -> [1 | 0x0] :Front
        Rear: [3 | 0x7fa3a0f05cb0] -> [2 | 0x0] :Front
        Rear:  [0 | 0x0] 
        Front: [0 | 0x0] 

        Size:     3
        Front:    10
        Is Empty: false
        Front:    20
        Is Empty: false
        Front:    30
        Is Empty: true

        Rear: [1 | 0x7fa3a0f05d00] -> [2 | 0x7fa3a0f05d00] -> [3 | 0x7fa3a0f05c90] -> [4 | 0x0] :Front

        [Desctructor call]
        	delete: [1 | 0x7fa3a0f05d00]
        	delete: [2 | 0x7fa3a0f05c90]
        	delete: [3 | 0x7fa3a0f05cb0]
        	delete: [4 | 0x0]
    */

    return 0;
}

Popularity 10/10 Helpfulness 2/10 Language cpp

Source: www.geeksforgeeks.org

Tags: c++

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Contributed on Jul 15 2023

Mysterious Macaque

0 Answers Avg Quality 2/10

Queue

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#include <iostream>
#include <queue>

using namespace std;

int main() {

  // create a queue of string
  queue<string> animals;

  // push elements into the queue
  animals.push("Cat");
  animals.push("Dog");
  
  cout << "Queue: ";

  // print elements of queue
  // loop until queue is empty
  while(!animals.empty()) {

    // print the element
    cout << animals.front() << ", ";

    // pop element from the queue
    animals.pop();
  }

  cout << endl;
 
  return 0;
}

Popularity 10/10 Helpfulness 1/10 Language cpp

Source: www.programiz.com

Tags: c++

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Contributed on May 24 2022

Enchanting Earthworm

0 Answers Avg Quality 2/10

queue

Comment

#include<stdio.h>
#include<stdlib.h>
 
struct queue
{
    int size;
    int f;
    int r;
    int* arr;
};
 
 
int isEmpty(struct queue *q){
    if(q->r==q->f){
        return 1;
    }
    return 0;
}
 
int isFull(struct queue *q){
    if(q->r==q->size-1){
        return 1;
    }
    return 0;
}
 
void enqueue(struct queue *q, int val){
    if(isFull(q)){
        printf("This Queue is full\n");
    }
    else{
        q->r++;
        q->arr[q->r] = val;
        printf("Enqued element: %d\n", val);
    }
}
 
int dequeue(struct queue *q){
    int a = -1;
    if(isEmpty(q)){
        printf("This Queue is empty\n");
    }
    else{
        q->f++;
        a = q->arr[q->f]; 
    }
    return a;
}
 
int main(){
    struct queue q;
    q.size = 4;
    q.f = q.r = 0;
    q.arr = (int*) malloc(q.size*sizeof(int));
    
    // Enqueue few elements
    enqueue(&q, 12);
    enqueue(&q, 15);
    enqueue(&q, 1); 
    printf("Dequeuing element %d\n", dequeue(&q));
    printf("Dequeuing element %d\n", dequeue(&q));
    printf("Dequeuing element %d\n", dequeue(&q)); 
    enqueue(&q, 45);
    enqueue(&q, 45);
    enqueue(&q, 45);
 
    if(isEmpty(&q)){
        printf("Queue is empty\n");
    }
    if(isFull(&q)){
        printf("Queue is full\n");
    }
 
    return 0;
}

Popularity 10/10 Helpfulness 1/10 Language c

Source: Grepper

Tags: c

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Contributed on Mar 14 2023

Aachman Agarwal

0 Answers Avg Quality 2/10

what is queue

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