C++ Queue Exercises: Union of two queues

C++ Queue: Exercise-27 with Solution

Write a C++ program to find the union of two queues.

Sample Solution:

C Code:

#include <iostream> // Including necessary library for input and output operations

using namespace std;

const int MAX_SIZE = 100; // Maximum size for the queue

class Queue {
private:
    int front; // Front of the queue
    int rear; // Rear of the queue
    int arr[MAX_SIZE]; // Array to store queue elements

public:
    Queue() {
        front = -1; // Initializing front index to -1
        rear = -1; // Initializing rear index to -1
    }

    bool isFull() {
        return (rear == MAX_SIZE - 1); // Check if the queue is full
    }

    bool isEmpty() {
        return (front == -1 && rear == -1); // Check if the queue is empty
    }

    void enqueue(int x) {
        if (isFull()) {
            cout << "Error: Queue is full" << endl; // Display error if the queue is full
            return;
        }
        if (isEmpty()) {
            front = 0;
            rear = 0;
        } else {
            rear++;
        }
        arr[rear] = x; // Add an element to the rear of the queue
    }

    void dequeue() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
            return;
        }
        if (front == rear) {
            front = -1;
            rear = -1;
        } else {
            front++;
        }
    }

    int peek() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
            return -1;
        }
        return arr[front]; // Return the element at the front of the queue
    }

    Queue find_Union(Queue q1, Queue q2) {
        Queue result; // Initialize a new queue to store the union

        // Copy all elements of q1 to result
        while (!q1.isEmpty()) {
            result.enqueue(q1.peek());
            q1.dequeue();
        }

        // Copy all unique elements of q2 to result
        while (!q2.isEmpty()) {
            int element = q2.peek();
            q2.dequeue();

            bool found = false;

            // Check if element already exists in result
            for (int i = result.front; i <= result.rear; i++) {
                if (result.arr[i] == element) {
                    found = true;
                    break;
                }
            }

            // If element not found in result, enqueue it
            if (!found) {
                result.enqueue(element);
            }
        }

        return result; // Return the resulting queue containing the union
    }

    void display() {
        if (isEmpty()) {
            cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
            return;
        }
        cout << "Queue elements are: ";
        for (int i = front; i <= rear; i++) {
            cout << arr[i] << " "; // Display all elements in the queue
        }
        cout << endl;
    }
};

int main() {
    cout << "Initialize three Queues." << endl;
    Queue q1, q2, q3; // Creating instances of Queue
    q1.enqueue(1);
    q1.enqueue(2);
    q1.enqueue(3);
    q2.enqueue(1);
    q2.enqueue(2);
    q2.enqueue(4);
    q3.enqueue(3);
    q3.enqueue(2);
    q3.enqueue(1);
    cout << "Queue-1" << endl;
    q1.display(); // Display elements of Queue-1
    cout << "Queue-2" << endl;
    q2.display(); // Display elements of Queue-2
    cout << "Queue-3" << endl;
    q3.display(); // Display elements of Queue-3
    cout << "\nUnion of two queues q1 and q2:" << endl;
    Queue result = q1.find_Union(q1, q2); // Get union of q1 and q2
    result.display(); // Display the union
    cout << "\nUnion of two queues q2 and q3:" << endl;
    Queue result1 = q1.find_Union(q2, q3); // Get union of q2 and q3
    result1.display(); // Display the union
    cout << "\nUnion of two queues q3 and q1:" << endl;
    Queue result2 = q1.find_Union(q3, q1); // Get union of q3 and q1
    result2.display(); // Display the union
    return 0;
}

Sample Output:

Initialize three Queues.
Queue-1
Queue elements are: 1 2 3 
Queue-2
Queue elements are: 1 2 4 
Queue-3
Queue elements are: 3 2 1 

Union of two queues q1 and q2:
Queue elements are: 1 2 3 4 

Union of two queues q2 and q3:
Queue elements are: 1 2 4 3 

Union of two queues q3 and q1:
Queue elements are: 3 2 1 

Flowchart:

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Previous C++ Exercise: Intersection of two queues.