Implement Queue using Linked List.cpp

/*
Implement Queue using Linked List
=================================

Implement a Queue using Linked List. 
A Query Q is of 2 Types
(i) 1 x   (a query of this type means  pushing 'x' into the queue)
(ii) 2     (a query of this type means to pop an element from the queue and print the poped element)

Example 1:
Input:
Q = 5
Queries = 1 2 1 3 2 1 4 2
Output: 2 3
Explanation: n the first testcase
1 2 the queue will be {2}
1 3 the queue will be {2 3}
2   poped element will be 2 the
    queue will be {3}
1 4 the queue will be {3 4}
2   poped element will be 3.

Example 2:
Input:
Q = 4
Queries = 1 2 2 2 1 3 
Output: 2 -1
Explanation: In the second testcase 
1 2 the queue will be {2}
2   poped element will be {2} then
    the queue will be empty. 
2   the queue is empty and hence -1
1 3 the queue will be {3}.

Your Task:
Complete the function push() which takes an integer as input parameter and pop() which will remove and return an element(-1 if queue is empty).

Expected Time Complexity: O(1).
Expected Auxiliary Space: O(1).

Constraints:
1 <= Q <= 100
1 <= x <= 100
*/

/* Structure of a node in Queue
struct QueueNode
{
    int data;
    QueueNode *next;
    QueueNode(int a)
    {
        data = a;
        next = NULL;
    }
};

And structure of MyQueue
struct MyQueue {
    QueueNode *front;
    QueueNode *rear;
    void push(int);
    int pop();
    MyQueue() {front = rear = NULL;}
}; */

//Function to push an element into the queue.
void MyQueue::push(int x)
{
  QueueNode *nN = new QueueNode(x);
  if (!front && !rear)
  {
    front = nN;
    rear = nN;
  }
  else
  {
    rear->next = nN;
    rear = nN;
  }
}

//Function to pop front element from the queue.
int MyQueue ::pop()
{
  if (front == NULL)
    return -1;
  int ans = front->data;
  if (front == rear)
  {
    front = NULL;
    rear = NULL;
  }
  else
  {
    front = front->next;
  }
  return ans;
}