Question

Implement a Queue ADT using a circular arraywith 5 string elements.Create

a Queue object and try various operations below, in C++.

Queue myQueue;

myQueue.enqueue(“Computer 1”);

myQueue.enqueue(“Computer 2”);

myQueue.enqueue(“Computer 3”);

myQueue.dequeue();

myQueue.enqueue(“Computer 4”);

myQueue.enqueue(“Computer 5”);

string course = myQueue.front(); // computer should be Comp 2

size = myQueue.size();// size should be 4

// output course and size

Answer 1

#include <iostream>

using namespace std;

class Queue {

        string *arr;
        int queueFront;
        int queueRear;
        int capacity;
        int numElements;

        void grow(int newsize) {
                string *newArray = new string[newsize];
                int count = 0;

                if (queueRear >= queueFront) {
                        for (int i = queueFront; i <= queueRear; i++) {
                                newArray[count++] = arr[i];
                        }
                } else {
                        for (int i = queueFront; i < capacity; i++) {
                                newArray[count++] = arr[i];
                        }
                        for (int i = 0; i <= queueRear; i++) {
                                newArray[count++] = arr[i];
                        }
                }

                if(count == 0) {
                        queueFront = queueRear = -1;
                } else {
                        queueFront = 0;
                        queueRear = count - 1;
                }

                capacity = newsize;
                delete [] arr;
                arr = newArray;
        }

        public:

        Queue() {
                capacity = 100;         
                arr = new string[capacity];
                queueFront = -1;
                queueRear = -1;
                numElements = 0;
        }

        void enqueue(string value) {
                if ((queueFront == 0 && queueRear == capacity-1) ||
                        (queueRear == (queueFront-1)%(capacity-1))) {
                        //Queue is Full
                        grow(2 * capacity);
                        enqueue(value);
                        return;
                } else if(queueFront == -1) {
                        // empty queue
                        queueFront = queueRear = 0;
                        arr[queueRear] = value;
                }  else if(queueRear == capacity-1 && queueFront != 0) {
                        queueRear = 0;
                        arr[queueRear] = value;
                }  else {
                        queueRear += 1;
                        arr[queueRear] = value;
                }
                numElements++;
        }

        string dequeue() {
                if(queueFront == -1) {
                        return NULL;
                }
                string data = arr[queueFront];
                
                if(queueFront == queueRear) {
                        // single element
                        queueFront = -1;
                        queueRear = -1;
                } else if (queueFront == capacity-1) {
                        queueFront = 0;
                } else {
                        queueFront++;
                }
                numElements--;
                return data;
        }

        // Just returns the front element O(1)
        string front() {
                if(queueFront != -1) {
                        return arr[queueFront];
                } else {
                        return NULL;
                }
        }

        int size() {
                return numElements;
        }
};

int main() {
        Queue myQueue;

        myQueue.enqueue("Computer 1");
        myQueue.enqueue("Computer 2");
        myQueue.enqueue("Computer 3");
        myQueue.dequeue();
        myQueue.enqueue("Computer 4");
        myQueue.enqueue("Computer 5");

        string course = myQueue.front(); // computer should be Comp 2

        int size = myQueue.size();// size should be 4

        // output course and size
        cout << course << endl;
        cout << size << endl;
}

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