C++ Queue Exercises: Remove all elements greater than a number from a queue

C++ Queue: Exercise-18 with Solution

Write a C++ program to remove all elements greater than a number from a queue.

Sample Solution:

C Code:

#include <iostream> // Including the 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
        }

        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;
        }  

        // Function to remove elements greater than a given limit
        void remove_greater_than(Queue& q, int limit) {
            if (q.isEmpty()) {
                cout << "Error: Queue is empty" << endl; // Display error if the queue is empty
                return;
            }
            int i = q.front;
            while (i <= q.rear) {
                if (q.arr[i] > limit) {
                    for (int j = i; j < q.rear; j++) {
                        q.arr[j] = q.arr[j + 1]; // Remove element by shifting subsequent elements
                    }
                    q.rear--; // Decrement the rear pointer
                }
                else {
                    i++;
                }
            }
        }
};

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 elements of the said queue greater than 3:" << endl;
    q.remove_greater_than(q, 4); // Remove elements greater than 3
    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 elements of the said queue greater than 3:
Queue elements are: 1 2 3 1 

Flowchart:

CPP Code Editor:

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