CBSE Class 12 Computer Science Chapter 10: Queue NCERT Solutions

The `delque()` function removes an element from the front of the linked queue. It first checks if the queue is empty by verifying if the `front` pointer is NULL. If the queue is not empty, it stores the current `front` node in a temporary pointer, prints the data of the element being deleted, updates the `front` pointer to the next node in the list, and then deallocates the memory occupied by the temporary node. If the queue becomes empty after deletion (i.e., `front` becomes NULL), the `rear` pointer is also set to NULL.

void queue :: delque ( ) { if ( front != NULL ) { node *Temp = front;

cout << Temp->name << " " << Temp->marks;

front = front->link;

delete Temp;

if(front == NULL)

rear = NULL; } else

cout << "Queue is empty"; }

This question asks for the declaration of a linked queue and a function to delete a player's information. The deletion function, `QUEUEDEL`, takes the current `front` pointer and the data of the player to be deleted (though the provided solution doesn't use the `val` and `val2` parameters for deletion logic, it assumes deletion from the front). It checks if the queue is empty. If not, it uses a temporary pointer to hold the current `front`, updates `front` to point to the next node, deletes the temporary node, and returns the new `front` pointer. The parameters `val` and `val2` seem extraneous for a standard front-deletion operation in a linked queue as typically implemented.

// Necessary declarations for the Node and Queue class

struct node {

int PlayerNo;

char PlayerName[20];

node* Link; }; // Assuming a Queue class with front and rear pointers

class Queue {

node *front, *rear;

public:

Queue() { front = rear = NULL; }

// Other functions like enqueue, display, etc.

node* QUEUEDEL(node* f_ptr); // Modified to take only front pointer for standard deletion }; // Function to delete a player's information from the front of the queue

node* Queue::QUEUEDEL(node* front_ptr) {

node* temp;

if (front_ptr == NULL) {

cout Link;

delete temp;

// If the queue becomes empty, update rear as well (assuming rear is a member variable)

if (front_ptr == NULL) {

rear = NULL; // This line would be inside the class method if 'rear' is a member } }

return front_ptr; // Return the updated front pointer } /*

Note: The original provided solution snippet `Node *QUEUEDEL(Node * front, int val, char val2[])`

and its implementation `temp®PlayerNo=val; strcpy (temp®PlayerName, val2);`

suggested modifying the node's data before deletion, which is unusual for a delete operation.

The rewritten solution above assumes a standard dequeue operation that removes the front element.

If the intention was to delete a specific player by value, the logic would be different and require searching the list. */

The `QDELETE()` function is designed to remove a passenger's record from the front of a linked queue. It first checks if the queue is empty by examining the `front` pointer. If the queue is not empty, a temporary pointer `Temp` is used to point to the current `front` node. The function then proceeds to update the `front` pointer to the next node in the sequence (`front->Link`). After that, the memory occupied by the node pointed to by `Temp` is deallocated using `delete Temp`. A crucial step is to check if the queue becomes empty after this deletion; if `front` is now NULL, it means the last element was removed, and `rear` should also be set to NULL to reflect the empty state of the queue. If the queue was initially empty, an appropriate message is displayed.

// Assuming 'front' and 'rear' are member pointers of a Queue class

// struct node { long int Pno; char Pname [20]; node *Link; };

void Queue::QDELETE( ) { node *Temp;

if ( front != NULL ) // Check if the queue is not empty { Temp = front; // Store the current front node in Temp

cout << "Deleting Passenger No: " << Temp->Pno << ", Name: " << Temp->Pname;

front = front->Link; // Move front to the next node

delete Temp; // Deallocate the memory of the deleted node

// If the queue becomes empty after deletion, update rear pointer

if ( front == NULL ) { rear = NULL; } cout << "\nPassenger deleted successfully."; } else { cout << "Queue is empty. Cannot delete."; } }