C++ Queue Exercises: Remove all duplicate elements from a queue

C++ Queue: Exercise-17 with Solution

Write a C++ program to remove all duplicate elements from a queue.

Sample Solution:

C Code:

 #include <iostream>

using namespace std;

const int MAX_SIZE = 100;

class Queue {
    private:
        int front; // Index of the front element in the queue
        int rear; // Index of the rear element in the queue
        int arr[MAX_SIZE]; // Array to hold 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); // Checks if the queue is full
        }

        bool isEmpty() {
            return (front == -1 && rear == -1); // Checks 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; // Adds 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]; // Returns the element at the front of the queue
        }

        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] << " "; // Displays all elements in the queue
            }
            cout << endl;
        }  

        void remove_duplicates(Queue &q) {
            if (q.isEmpty()) {
                cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
                return;
            }
            int n = q.rear - q.front + 1; // Calculate the number of elements in the queue
            int uniqueElements[n]; // Array to store unique elements
            int idx = 0;
            for (int i = q.front; i <= q.rear; i++) {
                bool isDuplicate = false;
                for (int j = q.front; j < i; j++) {
                    if (q.arr[i] == q.arr[j]) {
                        isDuplicate = true; // Check if the element is a duplicate
                        break;
                    }
                }
                if (!isDuplicate) {
                    uniqueElements[idx] = q.arr[i]; // Store unique elements
                    idx++;
                }
            }
            q.front = 0;
            q.rear = idx - 1;
            for (int i = 0; i < idx; i++) {
                q.arr[i] = uniqueElements[i]; // Update the queue with unique elements
            }
        }
};

int main() {
    cout << "Initialize a Queue." << endl;
    Queue q;
    cout << "\nInsert some elements into the queue:" << endl;
    q.enqueue(1);
    q.enqueue(2);
    q.enqueue(3);
    q.enqueue(5);
    q.enqueue(5);
    q.enqueue(6);
    q.enqueue(1);
    q.display();
    cout << "\nRemove all duplicates from the said queue:" << endl;
    q.remove_duplicates(q);
    q.display();
    return 0;
}

Sample Output:

Initialize a Queue.

Insert some elements into the queue:
Queue elements are: 1 2 3 5 5 6 1 

Remove all duplicates from the said queue:
Queue elements are: 1 2 3 5 6 

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Remove all odd elements from a queue.
Next C++ Exercise: Remove all elements greater than a number from a queue.