C++ Queue Exercises: Remove a given element from a queue

C++ Queue: Exercise-13 with Solution

Write a C++ program to remove a given element from a queue.

Sample Solution:

C Code:

#include <iostream>

#include <map>
#include <cmath>

using namespace std;

const int MAX_SIZE = 100;

class Queue {
  private:
    int front; // Holds the front index of the queue
    int rear; // Holds the rear index of the queue
    int arr[MAX_SIZE]; // Array to hold queue elements

  public:
    Queue() {
      front = -1; // Initialize front index to -1
      rear = -1; // Initialize 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; // Displays 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; // Displays 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; // Displays 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; // Displays 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_element(Queue & q, int x) {
      Queue temp; // Temporary queue to hold elements while removing the specified element
      bool found = false; // Flag to indicate if the element is found

      while (!q.isEmpty()) {
        int curr = q.peek();
        q.dequeue();

        if (curr == x) {
          found = true; // Element to be removed is found
          continue; // Skip adding this element to the temporary queue
        }

        temp.enqueue(curr); // Add elements other than the one to be removed to the temporary queue
      }

      if (!found) {
        cout << "Error: Element not found in queue" << endl; // Element not found in the queue
        return;
      }

      while (!temp.isEmpty()) {
        int curr = temp.peek();
        temp.dequeue();
        q.enqueue(curr); // Re-add elements back to the original queue from the temporary queue
      }
    }

};

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(4);
  q.enqueue(5);
  q.enqueue(6);
  q.display();
  cout << "\nRemove 5 from the said queue:" << endl;
  q.remove_element(q, 5);
  q.display();
  cout << "\nRemove 1 from the said queue:" << endl;
  q.remove_element(q, 1);
  q.display();
  cout << "\nRemove 6 from the said queue:" << endl;
  q.remove_element(q, 6);
  q.display();
  return 0;
}

Sample Output:

Initialize a Queue.

Insert some elements into the queue:
Queue elements are: 1 2 3 4 5 6 

Remove 5 from the said queue:
Queue elements are: 1 2 3 4 6 

Remove 1 from the said queue:
Queue elements are: 2 3 4 6 

Remove 6 from the said queue:
Queue elements are: 2 3 4 

Flowchart:

CPP Code Editor:

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Previous C++ Exercise: Find the second lowest element of a queue.
Next C++ Exercise: Remove all the elements from a queue.